using MSXML2;   

      public bool InterfaceEnble()  
     {  
         string url = "http://localhost:81/WebServiceLogin.asmx";  
         XMLHTTP http = new XMLHTTP();  
         try  
         {  
             http.open("GET ", url, false, null, null);  
             http.send(null);  
             int iStatus = http.status;  
             //如果状态不为200，就是不能调用此接口  
             if (iStatus == )  
                 return true;  
         }  
         catch (Exception ex)  
         {  
             MessageBox.Show("接口调用失败," + ex);  
         }

         return false;  
     }

判断接口是否可用