public void DownFile(string filePath ,string fileName )

 {

  // filePath  文件路径 例如：/File/记录.xlsx 

  // fileName  文件名称 例如：记录.xlsx （要后缀哦）

 Encoding encoding; // 申明编码

 string outputFileName; // 输出名字

 Debug.Assert(HttpContext.ApplicationInstance.Request.UserAgent != null, "HttpContext.ApplicationInstance.Request.UserAgent != null");

 string browser = HttpContext.ApplicationInstance.Request.UserAgent.ToUpper();

 // 微软的浏览器和ie过滤

 if (browser.Contains("MS") && browser.Contains("IE"))

 {

 outputFileName = HttpUtility.UrlEncode(filePath);

 encoding = Encoding.Default;

 }

 //火狐

 else if (browser.Contains("FIREFOX"))

 {

 outputFileName = fileName;

 encoding = Encoding.GetEncoding("GB2312");

 }

 else

 {

 outputFileName = HttpUtility.UrlEncode(fileName);

 encoding = Encoding.Default;

 }

 string absoluFilePath = Server.MapPath(filePath); //获取上传文件路径

 FileStream fs = new FileStream(absoluFilePath, FileMode.Open);

 byte[] bytes = new byte[(int)fs.Length];

 fs.Read(bytes, , bytes.Length);

 fs.Close(); //关闭流，释放资源

 HttpContext.ApplicationInstance.Response.Clear();

 HttpContext.ApplicationInstance.Response.Buffer = true;

 HttpContext.ApplicationInstance.Response.ContentEncoding = encoding;

 HttpContext.ApplicationInstance.Response.AddHeader("Content-Disposition", string.Format("attachment; filename={0}", string.IsNullOrEmpty(outputFileName) ? DateTime.Now.ToString("yyyyMMddHHmmssfff") : outputFileName));

 Response.BinaryWrite(bytes);

 Response.Flush();

 HttpContext.ApplicationInstance.Response.End();

 }

前端HTML 写一个a标签就好：如 <a href='DownFile' target='_blank'>文件下载</a>