diff --git a/backend/internal/service/auth_service.go b/backend/internal/service/auth_service.go
index 104a3262..5a5ca03d 100644
--- a/backend/internal/service/auth_service.go
+++ b/backend/internal/service/auth_service.go
@@ -82,14 +82,18 @@ func (s *AuthService) RegisterWithVerification(ctx context.Context, email, passw
 
 	// 检查是否需要邮件验证
 	if s.settingService != nil && s.settingService.IsEmailVerifyEnabled(ctx) {
+		// 如果邮件验证已开启但邮件服务未配置，拒绝注册
+		// 这是一个配置错误，不应该允许绕过验证
+		if s.emailService == nil {
+			log.Println("[Auth] Email verification enabled but email service not configured, rejecting registration")
+			return "", nil, ErrServiceUnavailable
+		}
 		if verifyCode == "" {
 			return "", nil, ErrEmailVerifyRequired
 		}
 		// 验证邮箱验证码
-		if s.emailService != nil {
-			if err := s.emailService.VerifyCode(ctx, email, verifyCode); err != nil {
-				return "", nil, fmt.Errorf("verify code: %w", err)
-			}
+		if err := s.emailService.VerifyCode(ctx, email, verifyCode); err != nil {
+			return "", nil, fmt.Errorf("verify code: %w", err)
 		}
 	}
 
diff --git a/backend/internal/service/auth_service_register_test.go b/backend/internal/service/auth_service_register_test.go
index 940baae5..a31267ab 100644
--- a/backend/internal/service/auth_service_register_test.go
+++ b/backend/internal/service/auth_service_register_test.go
@@ -113,13 +113,27 @@ func TestAuthService_Register_Disabled(t *testing.T) {
 	require.ErrorIs(t, err, ErrRegDisabled)
 }
 
-func TestAuthService_Register_EmailVerifyRequired(t *testing.T) {
+func TestAuthService_Register_EmailVerifyEnabledButServiceNotConfigured(t *testing.T) {
 	repo := &userRepoStub{}
+	// 邮件验证开启但 emailCache 为 nil（emailService 未配置）
 	service := newAuthService(repo, map[string]string{
 		SettingKeyRegistrationEnabled: "true",
 		SettingKeyEmailVerifyEnabled:  "true",
 	}, nil)
 
+	// 应返回服务不可用错误，而不是允许绕过验证
+	_, _, err := service.RegisterWithVerification(context.Background(), "user@test.com", "password", "any-code")
+	require.ErrorIs(t, err, ErrServiceUnavailable)
+}
+
+func TestAuthService_Register_EmailVerifyRequired(t *testing.T) {
+	repo := &userRepoStub{}
+	cache := &emailCacheStub{} // 配置 emailService
+	service := newAuthService(repo, map[string]string{
+		SettingKeyRegistrationEnabled: "true",
+		SettingKeyEmailVerifyEnabled:  "true",
+	}, cache)
+
 	_, _, err := service.RegisterWithVerification(context.Background(), "user@test.com", "password", "")
 	require.ErrorIs(t, err, ErrEmailVerifyRequired)
 }