diff --git a/backend/api-gateway/src/main/java/com/deepdata/gateway/infrastructure/casdoor/CasdoorUserService.java b/backend/api-gateway/src/main/java/com/deepdata/gateway/infrastructure/casdoor/CasdoorUserService.java
index f0fb29d..7a5fae4 100644
--- a/backend/api-gateway/src/main/java/com/deepdata/gateway/infrastructure/casdoor/CasdoorUserService.java
+++ b/backend/api-gateway/src/main/java/com/deepdata/gateway/infrastructure/casdoor/CasdoorUserService.java
@@ -116,9 +116,9 @@ public class CasdoorUserService {
     private User createUser(IdTokenClaims claims, String username, LocalDateTime now) {
         User user = new User();
         user.setUsername(username);
-        // email 列有唯一约束：空串会互相冲突，空值统一落 NULL（NULL 不参与唯一约束）
+        // email 列 NOT NULL UNIQUE：空串会互相冲突，缺省按用户名合成占位 email
         String email = claims.email();
-        user.setEmail(email == null || email.isBlank() ? null : email.trim());
+        user.setEmail(email == null || email.isBlank() ? username + "@casdoor.local" : email.trim());
         user.setFullName(claims.name());
         // 本地密码不可用：随机占位（登录统一走 Casdoor，本地 BCrypt 仅迁移期兜底）
         user.setPasswordHash(new BCryptPasswordEncoder(10).encode(UUID.randomUUID().toString()));