本文转载自：http://www.cnblogs.com/weixing/archive/2012/02/27/2369567.html

protected void Button1_Click(object sender, EventArgs e)
  {
  /*
  微软为Response对象提供了一个新的方法TransmitFile来解决使用Response.BinaryWrite
  下载超过400mb的文件时导致Aspnet_wp.exe进程回收而无法成功下载的问题。
  代码如下：
  */

Response.ContentType = "application/x-zip-compressed";
  Response.AddHeader("Content-Disposition", "attachment;filename=z.zip");
  string filename = Server.MapPath("DownLoad/aaa.zip");
  Response.TransmitFile(filename);
  }

//WriteFile实现下载
  protected void Button2_Click(object sender, EventArgs e)
  {
  /*
  using System.IO;
   
  */

string fileName ="aaa.zip";//客户端保存的文件名
  string filePath=Server.MapPath("DownLoad/aaa.zip");//路径

FileInfo fileInfo = new FileInfo(filePath);
  Response.Clear();
  Response.ClearContent();
  Response.ClearHeaders();
  Response.AddHeader("Content-Disposition", "attachment;filename=" + fileName);
  Response.AddHeader("Content-Length", fileInfo.Length.ToString());
  Response.AddHeader("Content-Transfer-Encoding", "binary");
  Response.ContentType = "application/octet-stream";
  Response.ContentEncoding = System.Text.Encoding.GetEncoding("gb2312");
  Response.WriteFile(fileInfo.FullName);
  Response.Flush();
  Response.End();
  }

//WriteFile分块下载
  protected void Button3_Click(object sender, EventArgs e)
  {

string fileName = "aaa.zip";//客户端保存的文件名
  string filePath = Server.MapPath("DownLoad/aaa.zip");//路径

System.IO.FileInfo fileInfo = new System.IO.FileInfo(filePath);

if (fileInfo.Exists == true)
  {
  const long ChunkSize = 102400;//100K 每次读取文件，只读取100Ｋ，这样可以缓解服务器的压力
  byte[] buffer = new byte[ChunkSize];

Response.Clear();
  System.IO.FileStream iStream = System.IO.File.OpenRead(filePath);
  long dataLengthToRead = iStream.Length;//获取下载的文件总大小
  Response.ContentType = "application/octet-stream";
  Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName));
  while (dataLengthToRead > 0 && Response.IsClientConnected) 
  {
  int lengthRead = iStream.Read(buffer, 0, Convert.ToInt32(ChunkSize));//读取的大小
  Response.OutputStream.Write(buffer, 0, lengthRead);
  Response.Flush();
  dataLengthToRead = dataLengthToRead - lengthRead;
  }
  Response.Close();
  }
  }

//流方式下载
  protected void Button4_Click(object sender, EventArgs e)
  {
  string fileName = "aaa.zip";//客户端保存的文件名
  string filePath = Server.MapPath("DownLoad/aaa.zip");//路径

//以字符流的形式下载文件
  FileStream fs = new FileStream(filePath, FileMode.Open);
  byte[] bytes = new byte[(int)fs.Length];
  fs.Read(bytes, 0, bytes.Length);
  fs.Close();
  Response.ContentType = "application/octet-stream";
  //通知浏览器下载文件而不是打开
  Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8));
  Response.BinaryWrite(bytes);
  Response.Flush();
  Response.End();

}