string strPath=@"F:\a.xlsx";

XSSFWorkbook xssfworkbook = new XSSFWorkbook(strPath);

//加了数据之后

MemoryStream ms = new MemoryStream();

xssfworkbook.write（ms）;//写到内存流

再对ms操作的时候，提示ms已经关闭了，输出不到浏览器中

@fulai_xy: 换个方式下载可否？Response.Write（filePath）

@幻天芒: 可以啊 ，能写主要的代码吗？？

@fulai_xy: Response.WriteFile(filePath)就是主要代码。

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();

@幻天芒: 哦，这样也可以吧

我是这样的

  MemoryStream ms = new MemoryStream();
  workbook.Write(ms);//调用这个后会关于文件流，在HSSFWorkbook不会关闭所以在处理时应注意

   Response.Charset = "GB2312";
            Response.ContentEncoding = System.Text.Encoding.GetEncoding("GB2312");

            Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode("22.xlsx", Encoding.UTF8).ToString());
            Response.ContentType = "application/ms-excel";
            this.EnableViewState = false;
            //Response.Write(ms.ToString());
            Response.BinaryWrite(ms.ToArray());

不过有个问题 ，打开以保存的excel文件，总是会提示是否恢复此工作的内容

@fulai_xy: 试试去掉编码选项...还有ContentType，这两个会影响。