asp.net后台导出excel的方法：使用System.Web.HttpContext.Current.Response导出excel

protected void ToExcel(DataTable dt, string FileName)
    {
        StringBuilder sb = new StringBuilder();
        sb.Append("<style type=\"text/css\">");
        sb.Append("<!--");
        sb.Append(".text");
        sb.Append("{mso-style-parent:style0;");
        sb.Append("font-size:10.0pt;");
        sb.Append("font-family:\"Arial Unicode MS\", sans-serif;");
        sb.Append("mso-font-charset:0;");
        sb.Append(@"mso-number-format:\@;");
        sb.Append("text-align:center;");
        sb.Append("border:.5pt solid black;");
        sb.Append("white-space:normal;}");
        sb.Append("-->");
        sb.Append("</style>");
        sb.Append("<table cellspacing=\"0\" rules=\"all\" border=\"1\" style=\"border-collapse:collapse;\">");

        DataRow[] myRow = dt.Select();
        int i = 0;
        int cl = dt.Columns.Count;

        //定义标题
        sb.Append("<tr align=\"Center\" style=\"font-weight:bold;\">");
        sb.Append("<td colspan=\"" + cl + "\" style =\" height : 25px; font-size: 20pt;\">"+ DropEnterprise.SelectedItem + "</td>");
        sb.Append("</tr>");
        
        //定义中间标题
        sb.Append("<tr align=\"Center\" style=\"font-weight:bold;\">");
        sb.Append("<td >" + txtStart.Text + "</td>");
        for (i = 0; i < cl - 2; i++)
        {
            sb.Append("<td ></td>");
        }
        sb.Append("<td >" + DropEnterprise.SelectedItem + "</td>");
        sb.Append("</tr>");

        //定义字段名
        sb.Append("<tr align=\"Center\" style=\"font-weight:bold;\">");
        for (i = 0; i < cl; i++)
        {
            if (i == (cl - 1))
            {
                sb.Append("<td>" + dt.Columns[i].ColumnName.ToString() + "</td></tr>");
            }
            else
            {
                //ls_item += dt.Columns[i].ColumnName.ToString() + "\t";
                sb.Append("<td>" + dt.Columns[i].ColumnName.ToString() + "</td>");
            }
        }
        
        //定义数据
        foreach (DataRow row in myRow)
        {
            sb.Append("<tr align=\"Center\">");
            for (i = 0; i < cl; i++)
            {
                if (i == (cl - 1))
                {
                    sb.Append("<td>" + row[i].ToString() + "</td></tr>");
                }
                else
                {
                    //ls_item += dt.Columns[i].ColumnName.ToString() + "\t";
                    sb.Append("<td>" + row[i].ToString() + "</td>");
                }
            }
            
        }
        sb.Append("</table>");

        System.Web.HttpContext.Current.Response.Clear();
        System.Web.HttpContext.Current.Response.Charset = "GB2312";
        // System.Web.HttpContext.Current.Response.ContentEncoding = System.Text.Encoding.UTF8;
        // 添加头信息，为"文件下载/另存为"对话框指定默认文件名 
        System.Web.HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment; filename=" +  System.Web.HttpUtility.UrlEncode(FileName, System.Text.Encoding.UTF8) + ".xls");
        // 添加头信息，指定文件大小，让浏览器能够显示下载进度 
        // System.Web.HttpContext.Current.Response.AddHeader("Content-Length",sb.ToString());

        // 指定返回的是一个不能被客户端读取的流，必须被下载 
        System.Web.HttpContext.Current.Response.ContentType = "application/ms-excel";

        // 把文件流发送到客户端 
        System.Web.HttpContext.Current.Response.Write(sb.ToString());
        // 停止页面的执行 

        System.Web.HttpContext.Current.Response.End();     
    }