1，get方式

             string URI = "url";
            //实例化
            WebClient client = new WebClient();
           // client.UseDefaultCredentials = true;
            return Encoding.UTF8.GetString(client.DownloadData(URI));

2，post方式

             string URI = "url";
            string myParameters = "key=" + key + "&system_id=" + System_id + "";
            //实例化
            WebClient client = new WebClient();
          //  client.UseDefaultCredentials = true;
            client.Headers[HttpRequestHeader.ContentType] = "application/x-www-form-urlencoded";
            client.Encoding = Encoding.UTF8;
            return client.UploadString(URI, myParameters);