public static void HttpDown(string fileName, System.Web.UI.Page 
p_Page,string floder)
        {
            string path = fileName;
    
        //输出到客户端
FileInfo file = new FileInfo(path);
            
p_Page.Response.Clear();
            p_Page.Response.Charset = "GB2312";
  
          p_Page.Response.ContentEncoding = 
System.Text.Encoding.GetEncoding("GB2312");
            
//添加头信息,为"文件下载/另存为"对话框指定默认文件名 
p_Page.Response.AddHeader("Content-Disposition", "attachment; filename=" + 
p_Page.Server.UrlEncode(file.Name));
            //添加头信息,指定文件大小,让浏览器能够显示下载进度 
p_Page.Response.AddHeader("Content-Length", file.Length.ToString());
     
       //指定返回的是一个不能被客户端读取的流,必须被下载 
p_Page.Response.ContentType = 
"application/ms-excel";
            //把文件流发送到客户端 
p_Page.Response.WriteFile(file.FullName);
            
p_Page.Response.Flush();
            Directory.Delete(floder, true);
      
  }
原文:http://www.cnblogs.com/guozefeng/p/3584108.html