diff --git a/library/think/Db.php b/library/think/Db.php
index 8fa799eb..7edb6ed4 100644
--- a/library/think/Db.php
+++ b/library/think/Db.php
@@ -88,6 +88,10 @@ class Db
         }
         return self::$instance[$name];
     }
+    
+    public static function clear(){
+        self::$instance = null;
+    }
 
     /**
      * 数据库连接参数解析