public static void Download_Excel(DataTable dt,string filename)
        {
            System.Web.HttpContext.Current.Response.ContentEncoding = System.Text.Encoding.GetEncoding("GB2312");
            System.Web.HttpContext.Current.Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(filename + ".xls"));
            string str_column = "";
            string ls_item = "";
            int i = 0;
            foreach(DataColumn dc in dt.Columns)
            {
                str_column += "\t" + dc.ColumnName;
            }
            str_column = str_column.Remove(0,1) + "\n";
            System.Web.HttpContext.Current.Response.Write(str_column);

            foreach(DataRow row in dt.Rows) 
            { 
                //在当前行中，逐列获得数据，数据之间以\t分割，结束时加回车符\n 
                for(i=0;i<(dt.Columns.Count-1);i++) 
                    ls_item +=row[i].ToString().Replace("\"","“") + "\t";      
                ls_item += row[i].ToString().Replace("\"","“") +"\n"; 
                //当前行数据写入HTTP输出流，并且置空ls_item以便下行数据     
                System.Web.HttpContext.Current.Response.Write(ls_item); 
                ls_item=""; 
            }

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

------解决方案--------------------

导出EXCEL表
/////////////////////////////////////////////////////////////////////////////
System.Web.UI.WebControls.DataGrid dgr = new DataGrid();
dgr.DataSource = dt;
dgr.DataBind();	
HttpContext.Current.Response.AppendHeader("Content-Disposition", "attachment;filename=" + "" + DateTime.Now.ToShortDateString() +""+".xls"+"");
HttpContext.Current.Response.Charset = "gb-2312";  
HttpContext.Current.Response.ContentEncoding = System.Text.Encoding.Default;  
HttpContext.Current.Response.ContentType = "application/ms-excel/ms-word";  
System.IO.StringWriter tw = new System.IO.StringWriter() ;  
System.Web.UI.HtmlTextWriter hw = new System.Web.UI.HtmlTextWriter(tw);
dgr.RenderControl(hw);
dgr.Dispose();
HttpContext.Current.Response.Write(tw.ToString());  
HttpContext.Current.Response.End();

------解决方案--------------------
http://www.ebookit.cn/177.html