一、//TransmitFile实现下载
    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/z.zip");
        Response.TransmitFile(filename);
    }

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

        */
        string fileName = "asd.txt";//客户端保存的文件名
        string filePath = Server.MapPath("DownLoad/aaa.txt");//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();
    }

三、   //WriteFile分块下载
    protected void Button3_Click(object sender, EventArgs e)
    {
        string fileName = "aaa.txt";//客户端保存的文件名
        string filePath = Server.MapPath("DownLoad/aaa.txt");//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();
        }
    }

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

//----------------------------------------------------------

public void DownloadFile( System.Web.UI.Page WebForm,String FileNameWhenUserDownload ,String FileBody )
{

　　WebForm.Response.ClearHeaders();
　　WebForm.Response.Clear();
　　WebForm.Response.Expires = 0;
　　WebForm.Response.Buffer = true;
　　WebForm.Response.AddHeader("Accept-Language", "zh-tw");
　　//‘文件名称
　　WebForm.Response.AddHeader("content-disposition", "attachment; filename=‘"+System.Web.HttpUtility.UrlEncode(FileNameWhenUserDownload, System.Text.Encoding.UTF8)+"‘");
　　WebForm.Response.ContentType = "Application/octet-stream";
　　//‘文件内容
　　WebForm.Response.Write(FileBody);//-----------
    WebForm.Response.End();
}


//上面这段代码是下载一个动态产生的文本文件，若这个文件已经存在于服务器端的实体路径，则可以通过下面的函数：

public void DownloadFileByFilePath( System.Web.UI.Page WebForm,String FileNameWhenUserDownload ,String FilePath )
{
　　WebForm.Response.ClearHeaders();
　　WebForm.Response.Clear();
　　WebForm.Response.Expires = 0;
    WebForm.Response.Buffer = true;
　　WebForm.Response.AddHeader("Accept-Language", "zh-tw");
　　//文件名称
　　WebForm.Response.AddHeader("content-disposition", "attachment; filename=‘" + System.Web.HttpUtility.UrlEncode(FileNameWhenUserDownload, System.Text.Encoding.UTF8) +"‘" );
　　WebForm.Response.ContentType = "Application/octet-stream";
　　//文件内容
　　WebForm.Response.Write(System.IO.File.Rea}dAllBytes(FilePath));//---------
　　WebForm.Response.End();

｝

转载地址：http://www.cnblogs.com/Warmsunshine/archive/2011/03/05/1971521.html

转载C#文件下载的实现