string url = "http://www.***.com?id=123&username=test&userpwd=*****";  
WebRequest wRequest = WebRequest.Create(url);  
wRequest.Method = "GET";  
wRequest.ContentType = "text/html;charset=UTF-8";  
WebResponse wResponse = wRequest.GetResponse();  
Stream stream = wResponse.GetResponseStream();  
StreamReader reader = new StreamReader(stream, System.Text.Encoding.Default);  
string str = reader.ReadToEnd();   //url返回的值  
reader.Close();  
wResponse.Close();