diff --git a/backend/alembic/versions/20260227_0006_invite_codes_and_profile_referral.py b/backend/alembic/versions/20260227_0006_invite_codes_and_profile_referral.py
index 5867909..08c6180 100644
--- a/backend/alembic/versions/20260227_0006_invite_codes_and_profile_referral.py
+++ b/backend/alembic/versions/20260227_0006_invite_codes_and_profile_referral.py
@@ -20,7 +20,7 @@ def upgrade() -> None:
         """
         CREATE TABLE invite_codes (
             id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
-            code VARCHAR(8) NOT NULL UNIQUE,
+            code VARCHAR(8) NOT NULL UNIQUE CHECK (code ~ '^[ABCDEFGHJKMNPQRSTUVWXYZ23456789]{8}$'),
             owner_id UUID REFERENCES profiles(id) ON DELETE SET NULL,
             status VARCHAR(20) NOT NULL DEFAULT 'active' CHECK (status IN ('active', 'disabled', 'expired')),
             used_count INTEGER NOT NULL DEFAULT 0 CHECK (used_count >= 0),
@@ -153,7 +153,6 @@ def upgrade() -> None:
 
 
 def downgrade() -> None:
-    op.execute("DROP FUNCTION IF EXISTS public.create_profile_for_new_user()")
     op.execute(
         """
         CREATE OR REPLACE FUNCTION public.create_profile_for_new_user()
diff --git a/backend/tests/integration/test_auth_routes.py b/backend/tests/integration/test_auth_routes.py
index 72a21d6..b42b6b0 100644
--- a/backend/tests/integration/test_auth_routes.py
+++ b/backend/tests/integration/test_auth_routes.py
@@ -792,3 +792,96 @@ def test_password_reset_confirm_weak_password_returns_422() -> None:
         assert response.headers["content-type"].startswith("application/problem+json")
     finally:
         app.dependency_overrides = {}
+
+
+class TestInviteCodeSignup:
+    def test_signup_with_valid_invite_code_returns_202(self) -> None:
+        user = AuthUser(id="user-1", email="user@example.com")
+        token_response = SessionResponse(
+            access_token="access",
+            refresh_token="refresh",
+            expires_in=3600,
+            token_type="bearer",
+            user=user,
+        )
+        app.dependency_overrides[get_auth_service] = _override_auth_service(
+            FakeAuthService(token_response)
+        )
+
+        client = TestClient(app)
+        try:
+            response = client.post(
+                "/api/v1/auth/verifications",
+                json={
+                    "username": "demo",
+                    "email": "user@example.com",
+                    "password": "secret123",
+                    "invite_code": "A2B3C4D5",
+                },
+            )
+            assert response.status_code == 202
+            assert response.json() == {"email": "user@example.com"}
+        finally:
+            app.dependency_overrides = {}
+
+    def test_signup_with_invalid_invite_code_length_returns_422(self) -> None:
+        user = AuthUser(id="user-1", email="user@example.com")
+        token_response = SessionResponse(
+            access_token="access",
+            refresh_token="refresh",
+            expires_in=3600,
+            token_type="bearer",
+            user=user,
+        )
+        app.dependency_overrides[get_auth_service] = _override_auth_service(
+            FakeAuthService(token_response)
+        )
+
+        client = TestClient(app)
+        try:
+            response = client.post(
+                "/api/v1/auth/verifications",
+                json={
+                    "username": "demo",
+                    "email": "user@example.com",
+                    "password": "secret123",
+                    "invite_code": "ABC123",
+                },
+            )
+            assert response.status_code == 422
+            assert response.headers["content-type"].startswith(
+                "application/problem+json"
+            )
+        finally:
+            app.dependency_overrides = {}
+
+    def test_signup_with_invalid_invite_code_chars_returns_422(self) -> None:
+        user = AuthUser(id="user-1", email="user@example.com")
+        token_response = SessionResponse(
+            access_token="access",
+            refresh_token="refresh",
+            expires_in=3600,
+            token_type="bearer",
+            user=user,
+        )
+        app.dependency_overrides[get_auth_service] = _override_auth_service(
+            FakeAuthService(token_response)
+        )
+
+        client = TestClient(app)
+        try:
+            response = client.post(
+                "/api/v1/auth/verifications",
+                json={
+                    "username": "demo",
+                    "email": "user@example.com",
+                    "password": "secret123",
+                    "invite_code": "ABCD1234",
+                },
+            )
+            assert response.status_code == 422
+            assert response.headers["content-type"].startswith(
+                "application/problem+json"
+            )
+        finally:
+            app.dependency_overrides = {}
diff --git a/docs/runtime/runtime-route.md b/docs/runtime/runtime-route.md
index 066e27d..be48a8f 100644
--- a/docs/runtime/runtime-route.md
+++ b/docs/runtime/runtime-route.md
@@ -20,7 +20,8 @@
   "username": "string (3-30 chars)",
   "email": "string (email)",
   "password": "string (min 6 chars)",
-  "redirect_to": "string? (optional)"
+  "redirect_to": "string? (optional)",
+  "invite_code": "string? (8 chars, 排除易混淆字符 0/1/I/L/O)"
 }
 ```
 
@@ -31,6 +32,12 @@
 }
 ```
 
+**邀请码说明：**
+- 可选字段，不填则注册不受影响
+- 格式：8 位字母数字组合，排除易混淆字符 (0, 1, I, L, O)
+- 注册时传入有效邀请码会建立邀请关系并增加邀请码使用次数
+- 无效邀请码（不存在/已禁用/已过期/已达上限）不会阻断注册成功
+
 **Errors:**
 - 422: 请求参数无效
 - 429: 请求过于频繁
diff --git a/docs/runtime/runtime-runbook.md b/docs/runtime/runtime-runbook.md
index a0deb93..1cca722 100644
--- a/docs/runtime/runtime-runbook.md
+++ b/docs/runtime/runtime-runbook.md
@@ -245,3 +245,4 @@ docker compose --env-file .env -f infra/docker/docker-compose.yml up -d --force-
 | 2026-02-25 | 重构为运维分层手册：Bootstrap Gate、分层验证、故障与回滚流程 |
 | 2026-02-25 | 新增配置漂移故障条目：修复 Auth 邮件模板失效与 signup 超时场景 |
 | 2026-02-27 | 用户搜索支持邮箱精确匹配：query 含 @ 符号时走 auth.users → profiles 两步查询 |
+| 2026-02-28 | 邀请码功能：新增 invite_codes 表、profiles.referred_by，注册时可选填邀请码并记录邀请关系 |