diff --git a/internal/service/role/service.go b/internal/service/role/service.go
index 1481ae8..867aa03 100644
--- a/internal/service/role/service.go
+++ b/internal/service/role/service.go
@@ -223,10 +223,19 @@ func (s *Service) AssignPermissions(ctx context.Context, roleID uint, permIDs []
 		return nil, errors.New(errors.CodeInvalidParam, fmt.Sprintf("权限 %v 不适用于此角色类型", invalidPermIDs))
 	}
 
+	// 批量获取已有权限集合，避免逐条 Exists 查询
+	existingPermIDs, err := s.rolePermissionStore.GetPermIDsByRoleID(ctx, roleID)
+	if err != nil {
+		return nil, errors.Wrap(errors.CodeInternalError, err, "获取已有权限失败")
+	}
+	existingSet := make(map[uint]bool, len(existingPermIDs))
+	for _, id := range existingPermIDs {
+		existingSet[id] = true
+	}
+
 	var rps []*model.RolePermission
 	for _, permID := range permIDs {
-		exists, _ := s.rolePermissionStore.Exists(ctx, roleID, permID)
-		if exists {
+		if existingSet[permID] {
 			continue
 		}
 
diff --git a/internal/store/postgres/role_permission_store.go b/internal/store/postgres/role_permission_store.go
index 20e6eaf..8ae83be 100644
--- a/internal/store/postgres/role_permission_store.go
+++ b/internal/store/postgres/role_permission_store.go
@@ -23,9 +23,13 @@ func NewRolePermissionStore(db *gorm.DB, redisClient *redis.Client) *RolePermiss
 	}
 }
 
-// Create 创建角色-权限关联
+// Create 创建角色-权限关联，唯一约束冲突时幂等处理
 func (s *RolePermissionStore) Create(ctx context.Context, rp *model.RolePermission) error {
 	if err := s.db.WithContext(ctx).Create(rp).Error; err != nil {
+		// 并发竞态导致唯一约束冲突，视为已存在，幂等返回
+		if isUniqueViolation(err) {
+			return nil
+		}
 		return err
 	}
 	s.clearRoleUsersCaches(ctx, rp.RoleID)