diff --git a/core/backend/apps/accounts/migrations/0003_invitation.py b/core/backend/apps/accounts/migrations/0003_invitation.py
new file mode 100644
index 0000000..935f877
--- /dev/null
+++ b/core/backend/apps/accounts/migrations/0003_invitation.py
@@ -0,0 +1,38 @@
+# Generated by Django 5.1.15 on 2026-06-19 04:29
+
+import apps.accounts.models
+import django.db.models.deletion
+import uuid
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('accounts', '0002_loginsession_userpreference'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Invitation',
+            fields=[
+                ('id', models.UUIDField(default=uuid.uuid4, editable=False, primary_key=True, serialize=False)),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('updated_at', models.DateTimeField(auto_now=True)),
+                ('code', models.CharField(default=apps.accounts.models._gen_invite_code, max_length=32, unique=True)),
+                ('role', models.CharField(choices=[('owner', 'Owner'), ('admin', 'Admin'), ('member', 'Member'), ('viewer', 'Viewer')], default='member', max_length=24)),
+                ('email', models.EmailField(blank=True, max_length=254)),
+                ('monthly_credit_limit', models.DecimalField(decimal_places=2, default=0, max_digits=12)),
+                ('expires_at', models.DateTimeField(default=apps.accounts.models._default_invite_expiry)),
+                ('used_at', models.DateTimeField(blank=True, null=True)),
+                ('status', models.CharField(choices=[('pending', 'Pending'), ('used', 'Used'), ('revoked', 'Revoked'), ('expired', 'Expired')], default='pending', max_length=16)),
+                ('created_by', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='created_invitations', to=settings.AUTH_USER_MODEL)),
+                ('team', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='invitations', to='accounts.team')),
+                ('used_by', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='used_invitations', to=settings.AUTH_USER_MODEL)),
+            ],
+            options={
+                'indexes': [models.Index(fields=['team', 'status'], name='accounts_in_team_id_b48ad1_idx')],
+            },
+        ),
+    ]
diff --git a/core/backend/apps/accounts/models.py b/core/backend/apps/accounts/models.py
index 3c8fc35..388a32a 100644
--- a/core/backend/apps/accounts/models.py
+++ b/core/backend/apps/accounts/models.py
@@ -95,3 +95,53 @@ class TeamMember(TimeStampedModel):
 
     def __str__(self) -> str:
         return f"{self.team} / {self.user} / {self.role}"
+
+
+def _gen_invite_code() -> str:
+    import secrets
+    import string
+
+    alphabet = "".join(c for c in (string.ascii_uppercase + string.digits) if c not in "O0I1")
+    block = lambda: "".join(secrets.choice(alphabet) for _ in range(4))  # noqa: E731
+    return f"TEAM-{block()}-{block()}"
+
+
+def _default_invite_expiry():
+    from datetime import timedelta
+
+    from django.utils import timezone
+
+    return timezone.now() + timedelta(days=7)
+
+
+class Invitation(TimeStampedModel):
+    """团队邀请码:超管/团管生成,新用户凭码注册即加入该团队(幂等加成员、不重复发额度)。"""
+
+    class Status(models.TextChoices):
+        PENDING = "pending", "Pending"
+        USED = "used", "Used"
+        REVOKED = "revoked", "Revoked"
+        EXPIRED = "expired", "Expired"
+
+    team = models.ForeignKey(Team, on_delete=models.CASCADE, related_name="invitations")
+    code = models.CharField(max_length=32, unique=True, default=_gen_invite_code)
+    role = models.CharField(max_length=24, choices=TeamMember.Role.choices, default=TeamMember.Role.MEMBER)
+    email = models.EmailField(blank=True)
+    monthly_credit_limit = models.DecimalField(max_digits=12, decimal_places=2, default=0)
+    created_by = models.ForeignKey(User, on_delete=models.SET_NULL, null=True, blank=True, related_name="created_invitations")
+    expires_at = models.DateTimeField(default=_default_invite_expiry)
+    used_by = models.ForeignKey(User, on_delete=models.SET_NULL, null=True, blank=True, related_name="used_invitations")
+    used_at = models.DateTimeField(null=True, blank=True)
+    status = models.CharField(max_length=16, choices=Status.choices, default=Status.PENDING)
+
+    class Meta:
+        indexes = [models.Index(fields=["team", "status"])]
+
+    @property
+    def is_valid(self) -> bool:
+        from django.utils import timezone
+
+        return self.status == self.Status.PENDING and self.expires_at > timezone.now()
+
+    def __str__(self) -> str:
+        return f"{self.team} / {self.code} / {self.status}"
diff --git a/core/backend/apps/accounts/serializers.py b/core/backend/apps/accounts/serializers.py
index 4a23ac4..b391084 100644
--- a/core/backend/apps/accounts/serializers.py
+++ b/core/backend/apps/accounts/serializers.py
@@ -2,7 +2,7 @@ from rest_framework import serializers
 
 from apps.billing.models import CreditAccount, CreditLedger
 
-from .models import LoginSession, Team, TeamMember, User, UserPreference
+from .models import Invitation, LoginSession, Team, TeamMember, User, UserPreference
 
 
 class UserSerializer(serializers.ModelSerializer):
@@ -59,45 +59,109 @@ class RegisterSerializer(serializers.Serializer):
     password = serializers.CharField(min_length=8, write_only=True)
     email = serializers.EmailField(required=False, allow_blank=True)
     team_name = serializers.CharField(max_length=128, required=False, allow_blank=True)
+    # 邀请码(可选):有效码 → 加入已有团队;空 → 开新团队当超管。认证定调:不用邮箱注册,username 为主标识。
+    invite_code = serializers.CharField(max_length=32, required=False, allow_blank=True)
 
     def validate_username(self, value):
         if User.objects.filter(username=value).exists():
             raise serializers.ValidationError("username already exists")
         return value
 
+    def validate_invite_code(self, value):
+        code = (value or "").strip().upper()
+        if not code:
+            return ""
+        from django.utils import timezone
+
+        from .models import Invitation
+
+        inv = Invitation.objects.filter(code=code).first()
+        if inv is None:
+            raise serializers.ValidationError("邀请码不存在")
+        if inv.status != Invitation.Status.PENDING:
+            raise serializers.ValidationError("邀请码已被使用或已撤销")
+        if inv.expires_at <= timezone.now():
+            raise serializers.ValidationError("邀请码已过期")
+        return code
+
     def create(self, validated_data):
         from decimal import Decimal
 
         from django.conf import settings
         from django.db import transaction
+        from django.utils import timezone
 
+        from .models import Invitation
+
+        invite_code = (validated_data.get("invite_code") or "").strip().upper()
         with transaction.atomic():
             user = User.objects.create_user(
                 username=validated_data["username"],
                 password=validated_data["password"],
                 email=validated_data.get("email", ""),
             )
-            team = Team.objects.create(
-                name=validated_data.get("team_name") or f"{user.username}'s Team",
-                owner=user,
-            )
-            TeamMember.objects.create(team=team, user=user, role=TeamMember.Role.OWNER)
-            trial = Decimal(str(settings.DEFAULT_TRIAL_CREDITS))
-            CreditAccount.objects.create(team=team, balance=trial)
-            # 开户赠送额度必须进流水,否则这笔钱在账单里查无凭证、无法对账(余额从第一条起就可追溯)
-            if trial > 0:
-                CreditLedger.objects.create(
+            if invite_code:
+                # 凭码加入已有团队:幂等加成员(避开 unique_together 撞 IntegrityError)、标邀请 used、
+                # 整段跳过 CreditAccount + ledger(团队级 OneToOne 已存在,二次建必报错、额度也不重发)。
+                inv = Invitation.objects.select_for_update().filter(code=invite_code).first()
+                if inv is None or inv.status != Invitation.Status.PENDING or inv.expires_at <= timezone.now():
+                    raise serializers.ValidationError({"invite_code": "邀请码已失效"})
+                team = inv.team
+                role = inv.role
+                if role == TeamMember.Role.OWNER:
+                    role = TeamMember.Role.ADMIN  # 不允许 OWNER(Team.owner 唯一)
+                TeamMember.objects.get_or_create(
                     team=team,
                     user=user,
-                    ledger_type=CreditLedger.Type.RECHARGE,
-                    amount=trial,
-                    balance_after=trial,
-                    reason="新用户试用额度赠送",
-                    metadata={"kind": "trial_grant"},
+                    defaults={
+                        "role": role,
+                        "status": TeamMember.Status.ACTIVE,
+                        "monthly_credit_limit": inv.monthly_credit_limit,
+                    },
                 )
+                inv.status = Invitation.Status.USED
+                inv.used_by = user
+                inv.used_at = timezone.now()
+                inv.save(update_fields=["status", "used_by", "used_at", "updated_at"])
+            else:
+                # 无码:开新团队当 owner + 发试用额度(原逻辑)
+                team = Team.objects.create(
+                    name=validated_data.get("team_name") or f"{user.username}'s Team",
+                    owner=user,
+                )
+                TeamMember.objects.create(team=team, user=user, role=TeamMember.Role.OWNER)
+                trial = Decimal(str(settings.DEFAULT_TRIAL_CREDITS))
+                CreditAccount.objects.create(team=team, balance=trial)
+                # 开户赠送额度必须进流水,否则这笔钱在账单里查无凭证、无法对账(余额从第一条起就可追溯)
+                if trial > 0:
+                    CreditLedger.objects.create(
+                        team=team,
+                        user=user,
+                        ledger_type=CreditLedger.Type.RECHARGE,
+                        amount=trial,
+                        balance_after=trial,
+                        reason="新用户试用额度赠送",
+                        metadata={"kind": "trial_grant"},
+                    )
         return {"user": user, "team": team}
 
 
+class InvitationSerializer(serializers.ModelSerializer):
+    used_by_username = serializers.CharField(source="used_by.username", read_only=True, default=None)
+    register_url = serializers.SerializerMethodField()
+
+    class Meta:
+        model = Invitation
+        fields = [
+            "id", "code", "role", "email", "monthly_credit_limit", "status",
+            "expires_at", "used_by", "used_by_username", "used_at", "created_at", "register_url",
+        ]
+        read_only_fields = fields
+
+    def get_register_url(self, obj):
+        return f"/register?invite={obj.code}"
+
+
 class LoginSerializer(serializers.Serializer):
     username = serializers.CharField()
     password = serializers.CharField(write_only=True)
diff --git a/core/backend/apps/accounts/tests.py b/core/backend/apps/accounts/tests.py
index f0a4a7e..e84f12b 100644
--- a/core/backend/apps/accounts/tests.py
+++ b/core/backend/apps/accounts/tests.py
@@ -47,3 +47,72 @@ class AuthApiTests(TestCase):
         self.assertEqual(genesis.first().amount, trial)
         self.assertEqual(genesis.first().balance_after, trial)  # 流水终点 == 账户余额,可对账
 
+
+class InvitationFlowTests(TestCase):
+    def _register(self, client, username, **extra):
+        return client.post(
+            "/api/auth/register/",
+            {"username": username, "password": "strong-password", **extra},
+            format="json",
+        )
+
+    def test_invite_join_same_team_no_duplicate_credits(self):
+        from apps.accounts.models import Invitation
+
+        owner_client = APIClient()
+        r = self._register(owner_client, "inv-owner", team_name="Owner Team")
+        self.assertEqual(r.status_code, 201)
+        team = Team.objects.get(name="Owner Team")
+        accounts_before = CreditAccount.objects.filter(team=team).count()
+        ledgers_before = CreditLedger.objects.filter(team=team).count()
+
+        # 超管生成邀请码
+        owner_client.credentials(HTTP_AUTHORIZATION=f"Token {r.data['token']}")
+        gen = owner_client.post(
+            "/api/auth/team/invitations/",
+            {"role": "member", "monthly_credit_limit": "500"},
+            format="json",
+        )
+        self.assertEqual(gen.status_code, 201)
+        code = gen.data["code"]
+        self.assertTrue(code.startswith("TEAM-"))
+
+        # 新用户凭码注册
+        r2 = self._register(APIClient(), "inv-joiner", invite_code=code)
+        self.assertEqual(r2.status_code, 201)
+        joiner = User.objects.get(username="inv-joiner")
+
+        # 进的是同一团队、角色对、active、额度对
+        member = TeamMember.objects.get(team=team, user=joiner)
+        self.assertEqual(member.role, TeamMember.Role.MEMBER)
+        self.assertEqual(member.status, TeamMember.Status.ACTIVE)
+        self.assertEqual(member.monthly_credit_limit, Decimal("500"))
+        # 没开新团队
+        self.assertFalse(Team.objects.filter(owner=joiner).exists())
+        # 关键:不重复发额度 —— 团队 CreditAccount/ledger 数量不变
+        self.assertEqual(CreditAccount.objects.filter(team=team).count(), accounts_before)
+        self.assertEqual(CreditLedger.objects.filter(team=team).count(), ledgers_before)
+        # 邀请标 used
+        inv = Invitation.objects.get(code=code)
+        self.assertEqual(inv.status, Invitation.Status.USED)
+        self.assertEqual(inv.used_by, joiner)
+
+    def test_register_with_unknown_invite_rejected(self):
+        r = self._register(APIClient(), "bad-inv", invite_code="TEAM-ABCD-EFGH")
+        self.assertEqual(r.status_code, 400)
+        self.assertFalse(User.objects.filter(username="bad-inv").exists())
+
+    def test_invite_generate_requires_manage_permission(self):
+        owner_client = APIClient()
+        ro = self._register(owner_client, "perm-owner", team_name="Perm Team")
+        owner_client.credentials(HTTP_AUTHORIZATION=f"Token {ro.data['token']}")
+        gen = owner_client.post("/api/auth/team/invitations/", {"role": "member"}, format="json")
+        code = gen.data["code"]
+
+        joiner_client = APIClient()
+        rj = self._register(joiner_client, "perm-member", invite_code=code)
+        # 普通成员尝试生成邀请码 → 403
+        joiner_client.credentials(HTTP_AUTHORIZATION=f"Token {rj.data['token']}")
+        gen2 = joiner_client.post("/api/auth/team/invitations/", {"role": "member"}, format="json")
+        self.assertEqual(gen2.status_code, 403)
+
diff --git a/core/backend/apps/accounts/urls.py b/core/backend/apps/accounts/urls.py
index 4b2fef0..a9acead 100644
--- a/core/backend/apps/accounts/urls.py
+++ b/core/backend/apps/accounts/urls.py
@@ -8,8 +8,10 @@ from .views import (
     me,
     preferences,
     register,
+    revoke_invitation,
     revoke_login_session,
     revoke_other_sessions,
+    team_invitations,
     team_member_detail,
     team_member_password,
     team_members,
@@ -31,4 +33,6 @@ urlpatterns = [
     path("team/members/", team_members, name="team-members"),
     path("team/members/<uuid:member_id>/", team_member_detail, name="team-member-detail"),
     path("team/members/<uuid:member_id>/password/", team_member_password, name="team-member-password"),
+    path("team/invitations/", team_invitations, name="team-invitations"),
+    path("team/invitations/<uuid:invite_id>/revoke/", revoke_invitation, name="team-invitation-revoke"),
 ]
diff --git a/core/backend/apps/accounts/views.py b/core/backend/apps/accounts/views.py
index a2edd29..512c49a 100644
--- a/core/backend/apps/accounts/views.py
+++ b/core/backend/apps/accounts/views.py
@@ -12,8 +12,9 @@ from rest_framework.response import Response
 
 from apps.common.api import get_current_team
 
-from .models import LoginSession, TeamMember, User, UserPreference
+from .models import Invitation, LoginSession, TeamMember, User, UserPreference
 from .serializers import (
+    InvitationSerializer,
     LoginSerializer,
     LoginSessionSerializer,
     RegisterSerializer,
@@ -238,6 +239,45 @@ def team_members(request):
     return Response(TeamMemberSerializer(member).data, status=status.HTTP_201_CREATED)
 
 
+@api_view(["GET", "POST"])
+@permission_classes([IsAuthenticated])
+def team_invitations(request):
+    """团队邀请码:GET 列本团队邀请;POST 生成新码。权限=超管/团管(复用 can_manage_team)。"""
+    team = get_current_team(request.user)
+    if not can_manage_team(request.user, team):
+        return Response({"detail": "permission denied"}, status=status.HTTP_403_FORBIDDEN)
+    if request.method == "GET":
+        invites = team.invitations.select_related("used_by").order_by("-created_at")
+        return Response(InvitationSerializer(invites, many=True).data)
+    role = normalize_member_role(request.data.get("role"))
+    if role == TeamMember.Role.OWNER:
+        role = TeamMember.Role.ADMIN  # 邀请不允许 OWNER(Team.owner 唯一)
+    invite = Invitation.objects.create(
+        team=team,
+        role=role,
+        email=str(request.data.get("email") or "").strip(),
+        monthly_credit_limit=request.data.get("monthly_credit_limit") or request.data.get("monthly") or 0,
+        created_by=request.user,
+    )
+    return Response(InvitationSerializer(invite).data, status=status.HTTP_201_CREATED)
+
+
+@api_view(["POST"])
+@permission_classes([IsAuthenticated])
+def revoke_invitation(request, invite_id):
+    """撤销一个待用邀请码。权限=超管/团管。"""
+    team = get_current_team(request.user)
+    if not can_manage_team(request.user, team):
+        return Response({"detail": "permission denied"}, status=status.HTTP_403_FORBIDDEN)
+    invite = Invitation.objects.filter(team=team, id=invite_id).first()
+    if invite is None:
+        return Response({"detail": "not found"}, status=status.HTTP_404_NOT_FOUND)
+    if invite.status == Invitation.Status.PENDING:
+        invite.status = Invitation.Status.REVOKED
+        invite.save(update_fields=["status", "updated_at"])
+    return Response(InvitationSerializer(invite).data)
+
+
 @api_view(["PATCH", "DELETE"])
 @permission_classes([IsAuthenticated])
 def team_member_detail(request, member_id):