using System.IO;
using System.Text;
using System.Net;

按钮事件:

private void button5_Click(object sender, System.EventArgs e)
  {
   string DownloadUrl="                ";
  
   string LocalPath=Application.StartupPath.ToString()+"\\"+"qqwry"+DateTime.Now.ToShortDateString()+".rar";

   if(downfile(DownloadUrl,LocalPath))
   {
    MessageBox.Show("下载完成");
   }
   else
   {
    MessageBox.Show("下载过程中出现错误:");
   }  

  }

下载函数:
  public bool downfile(string url,string LocalPath)
  {
   try
   {
    Uri u = new Uri(url);
    HttpWebRequest mRequest = (HttpWebRequest)WebRequest.Create(u);
    mRequest.Method = "GET";
    mRequest.ContentType = "application/x-www-form-urlencoded";
    HttpWebResponse wr = (HttpWebResponse)mRequest.GetResponse();
    statusBar1.Text = "开始下载文件...";
    Stream sIn = wr.GetResponseStream();
    FileStream fs = new FileStream(LocalPath, FileMode.Create, FileAccess.Write);
    long length = wr.ContentLength;
    int i = 0;   
    long j=0;
    statusBar1.Text = "正在接收数据...";
    byte[] buffer = new byte[1024];
    while ((i = sIn.Read(buffer, 0, buffer.Length)) > 0)
    {
     j+=i;    
     fs.Write(buffer, 0,i);
     statusBar1.Text="文件大小:"+length.ToString()+"字节   当前下载:"+j+"字节";
   
    }

    sIn.Close();
    wr.Close();
    statusBar1.Text = "文件下载完毕...文件大小"+fs.Length.ToString()+"字节";
    fs.Close();
    return true;
   }
   catch { return false; }

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/xqf222/archive/2007/09/19/1790830.aspx