static CookieContainer GetCookie(string postString, string postUrl)
 {
 CookieContainer cookie = new CookieContainer();
 
 HttpWebRequest httpRequset = (HttpWebRequest)HttpWebRequest.Create(postUrl);//创建http 请求
httpRequset.CookieContainer = cookie;//设置cookie
httpRequset.Method = "POST";//POST 提交
 httpRequset.KeepAlive = true;
 httpRequset.UserAgent = "Mozilla/5.0 (Windows NT 6.3; WOW64; Trident/7.0; rv:11.0) like Gecko";
 httpRequset.Accept = "text/html, application/xhtml+xml, */*";
httpRequset.ContentType = "application/x-www-form-urlencoded";//以上信息在监听请求的时候都有的直接复制过来
byte[] bytes = System.Text.Encoding.UTF8.GetBytes(postString);
httpRequset.ContentLength = bytes.Length;
 Stream stream = httpRequset.GetRequestStream();
stream.Write(bytes, 0, bytes.Length);
 stream.Close();//以上是POST数据的写入
 HttpWebResponse httpResponse = (HttpWebResponse)httpRequset.GetResponse();//获得 服务端响应
 return cookie;//拿到cookie
 }

 static string GetContent(CookieContainer cookie, string url)
{
string content;
HttpWebRequest httpRequest = (HttpWebRequest)HttpWebRequest.Create(url);
httpRequest.CookieContainer = cookie;
httpRequest.Referer = url;
httpRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.3; WOW64; Trident/7.0; rv:11.0) like Gecko";
httpRequest.Accept = "text/html, application/xhtml+xml, */*";
httpRequest.ContentType = "application/x-www-form-urlencoded";
httpRequest.Method = "GET";
HttpWebResponse httpResponse = (HttpWebResponse)httpRequest.GetResponse();
using (Stream responsestream = httpResponse.GetResponseStream())
{ 
using (StreamReader sr = new StreamReader(responsestream, System.Text.Encoding.UTF8))
 {
 content = sr.ReadToEnd();
 }
}
 return content;
 }

static void Main(string[] args)
{
string loginstr = "{要post 的登陆数据包括用户名和密码}";
//从登陆的地址获取cookie
CookieContainer cookie = GetCookie(loginstr, "http://passport.cnblogs.com/login.aspx");
 //这个是进入后台地址
 Console.WriteLine(GetContent(cookie, "http://i.cnblogs.com/EditPosts.aspx"));
 Console.Read();
}