今天遇到了这个问题，记录下来，方便不知道的朋友以后用，当在生成Excel表格时直接将网页表格直接保存成excel文件后，用excel能打开表格中的数字自动用科学计数法表示了，比如table中的0.0在excel中显示为0。
解决方案如下。
protected void downloadButton_Click(object sender, EventArgs e)
{
BindPage();
Response.ClearContent();
string attachment = "attachment; filename=Payroll.xls";
Response.AddHeader("content-disposition", attachment);
Response.ContentType = "application/ms-excel";
StringWriter sw = new StringWriter();
HtmlTextWriter htw = new HtmlTextWriter(sw);
tabData.Border = 1;
tabData.RenderControl(htw);
string startHtml = "<html xmlns:o=\"urn:schemas-microsoft-com:office:office\" xmlns:x=\"urn:schemas-microsoft-com:office:excel\" xmlns=\"http://www.w3.org/TR/REC-html40\">";
string endHtml = "</html>";
Response.Write(startHtml + sw.NewLine + sw.ToString().Replace("<td align=\"right\" style=\"80px;\">","<td align=\"right\" style=\"80px;\" x:str>") + endHtml);
Response.End();
}