WebClient MyWebClient = new WebClient();
                 
MyWebClient.Credentials = CredentialCache.DefaultCredentials;//获取或设置用于向Internet资源的请求进行身份验证的网络凭据
Byte[] pageData = MyWebClient.DownloadData("http://www.baidu.com");
//string pageHtml = Encoding.Default.GetString(pageData); 
 FileStream file = new FileStream("C:\\test.html", FileMode.Create);
 file.Write(pageData, 0, pageData.Length);

private string GetWebClient(string url)
{
  string strHTML = "";
  WebClient myWebClient = new WebClient();
  Stream myStream = myWebClient.OpenRead(url);
  StreamReader sr = new StreamReader(myStream, System.Text.Encoding.GetEncoding("utf-8"));
  strHTML = sr.ReadToEnd();
  myStream.Close();
  return strHTML;
}

private string GetWebRequest(string url)
{
  Uri uri = new Uri(url);
  WebRequest myReq = WebRequest.Create(uri);
  WebResponse result = myReq.GetResponse();
  Stream receviceStream = result.GetResponseStream();
  StreamReader readerOfStream = new StreamReader(receviceStream, System.Text.Encoding.GetEncoding("utf-8"));
  string strHTML = readerOfStream.ReadToEnd();
  readerOfStream.Close();
  receviceStream.Close();
  result.Close();
  return strHTML;
}

private string GetHttpWebRequest(string url)
{
  Uri uri = new Uri(url);
  HttpWebRequest myReq = (HttpWebRequest)WebRequest.Create(uri);
  myReq.UserAgent = "User-Agent:Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705";
  myReq.Accept = "*/*";
  myReq.KeepAlive = true;
  myReq.Headers.Add("Accept-Language", "zh-cn,en-us;q=0.5");
  HttpWebResponse result = (HttpWebResponse)myReq.GetResponse();
  Stream receviceStream = result.GetResponseStream();
  StreamReader readerOfStream = new StreamReader(receviceStream, System.Text.Encoding.GetEncoding("utf-8"));
  string strHTML = readerOfStream.ReadToEnd();
  readerOfStream.Close();
  receviceStream.Close();
  result.Close();
  return strHTML;
}