页面存在多个AJAX的后台处理函数  

一PageLoad的时候,加入  
  if (Ajax() == true)  
   {
            return;
   }
二 Ajax()函数
    private bool Ajax()
    {
        bool Return = false;
        string senderCtl = "";
        if (Request["senderCtl"] != null)
        {
            senderCtl = Request["senderCtl"].ToString().Trim();
            switch (senderCtl)
            {
                case "DOM_dt":  //使用DOM返回DT的XML
                    Response.Write(this.GetDom_Dt());
                    break;
                case "DOM_Node"://使用DOM返回XML文件
                    Response.Write(this.GetXmlDoc());
                    break;
                case "Http_string"://使用HTTP返回字串
                    Response.Write(this.GetHttp_string());
                    break;
                default: break;
            }
            Response.Flush();
            Response.Close();
            Return = true;
        }
        else
        {
            Return = false;
        }

        return Return;
    }

三,前台
var weburl="Default.aspx?senderCtl=Http_string";