CookieContainer cc = new CookieContainer();
             Encoding encoding = System.Text.Encoding.Default;

             string postData = "tpl_ok=&next_target=&tpl=mn&skip_ok=&aid=&need_pay=&need_coin=&pay_method=&u=http%3A%2F%2Fwww.baidu.com%2F&return_method=get&more_param=&return_type=&psp_tt=0&password=wujingxing&safeflg=0&isphone=tpl&username=wjxdbd&verifycode=&mem_pass=on";
             byte[] byteArray = Encoding.encoding.GetBytes(postData); // 转化
                    HttpWebRequest webRequest2 = (HttpWebRequest)WebRequest.Create(new Uri("https://passport.baidu.com/?login"));
                    webRequest2.CookieContainer = cc;
            webRequest2.Method = "POST";
                    webRequest2.Accept="image/jpeg, application/x-ms-application, image/gif, application/xaml+xml, image/pjpeg, application/x-ms-xbap, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*";
                    webRequest2.ContentLength=byteArray.Length;
            
            
                    webRequest2.ContentType = "application/x-www-form-urlencoded";
                    webRequest2.Referer="https://passport.baidu.com/?login&tpl=mn";
                    webRequest2.UserAgent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0)";       
            
                   
            Stream newStream = webRequest2.GetRequestStream();
                    // Send the data.
                    newStream.Write(byteArray, 0, byteArray.Length);    //写入参数
                    newStream.Close();
                    //HttpWebResponse response2 = (HttpWebResponse)webRequest2.GetResponse();
                    //StreamReader sr2=new StreamReader(response2.GetResponseStream(), Encoding.Default);
                    //string text2 = sr2.ReadToEnd();
                    webBrowser1.Navigate("https://www.baidu.com/");