为什么导出来的Excel内容是乱码?看下我的代码吧.

private void ReBut5_Click(object sender, System.EventArgs e)
{
if(this.ReGrid1.Items.Count>0)
{
this.ButExcel("application/ms-excel","加班時間大於36小時.xls");
}
else
{
Page.RegisterStartupScript("","<script>alert('沒有資料導出!')</scrip>");
}
}
public void ButExcel(string FileType, string FileName)
{

System.IO.StringWriter tw= new System.IO.StringWriter();
System.Web.UI.HtmlTextWriter hw = new System.Web.UI.HtmlTextWriter(tw);
Response.Charset = "Big5";
Response.ContentEncoding = System.Text.Encoding.UTF8;
Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(FileName, System.Text.Encoding.UTF8).ToString());
Response.ContentType = FileType;
this.EnableViewState = false;
Response.Clear();
Response.Buffer= true;
DataGrid dg=new DataGrid();
SqlConnection Con = new SqlConnection(System.Configuration.ConfigurationSettings.AppSettings["Con"]);
Con.Open();
SqlDataAdapter sda = new SqlDataAdapter();
sda.SelectCommand = new SqlCommand("select WorkId as '工號',[name] as '姓名',FactTotal as '實際加班時數',dept as '部門' from V_ReportJB where facttotal > 36",Con);
DataSet ds = new DataSet();
sda.Fill(ds,"table");
dg.DataSource=ds;
dg.DataBind();
dg.RenderControl(hw);
Response.Write(tw.ToString());
Response.End();

}