一下段代码在登录chinahr.com是没问题，但是在登录51job.com时却不行。是什么原因？希望大伙能帮忙解决一下，哥们儿俺谢你了！

string.Format("username={0}&password={1}", this.Username, this.Password));其中的username和password是否是数据库中的字段？是不是因为51job的数据库中字段不是这样拼写的？因为我修改了password为userpassword后，登录chinahr.com也不成功。

我改怎么改才能登录51job.com.希望知道的朋友告诉我实现原理，在这先谢大家了。

      //根据url做登陆请求
                WebResponse responce = this.doPost(url,
                    string.Format("username={0}&password={1}", this.Username, this.Password));

  　　/// <summary>
        /// 发送Post类型请求
        /// </summary>
        /// <param name="url">请求地址</param>
        /// <param name="postData">参数</param>
        /// <returns></returns>
        public WebResponse doPost(string url, string postData)
        {
            try
            {
                byte[] paramByte = Encoding.Default.GetBytes(postData); // 转化
                HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(url);
                webRequest.Method = "POST";
                webRequest.ContentType = "application/x-www-form-urlencoded";
                webRequest.ContentLength = paramByte.Length;
                webRequest.CookieContainer = this.cookies;
                //webRequest.Timeout = 5000;
                Stream newStream = webRequest.GetRequestStream();
                newStream.Write(paramByte, 0, paramByte.Length);    //写入参数
                newStream.Close();
                return webRequest.GetResponse();
            }
            catch (Exception ce)
            {
                throw ce;
            }
        }