public static void HttpDown(string fileName, System.Web.UI.Page p_Page,string floder)
{
string path = fileName;
//輸出到客戶端
FileInfo file = new FileInfo(path);
p_Page.Response.Clear();
p_Page.Response.Charset = "GB2312";
p_Page.Response.ContentEncoding = System.Text.Encoding.GetEncoding("GB2312");
//添加頭信息，為"文件下載/另存為"對話框指定默認文件名
p_Page.Response.AddHeader("Content-Disposition", "attachment; filename=" + p_Page.Server.UrlEncode(file.Name));
//添加頭信息，指定文件大小，讓瀏覽器能夠顯示下載進度
p_Page.Response.AddHeader("Content-Length", file.Length.ToString());
//指定返回的是一個不能被客戶端讀取的流，必須被下載
p_Page.Response.ContentType = "application/ms-excel";
//把文件流發送到客戶端
p_Page.Response.WriteFile(file.FullName);
p_Page.Response.Flush();
Directory.Delete(floder, true);
}

c#下載文件案例