/// <summary>
/// 生成Excel文件
/// </summary>
/// <param name="ds">数据集</param>
/// <param name="fileName">生成文件名</param>
private void CreateExcel(DataTable dt, string fileName)
{
    HttpResponse resp;
    resp = Page.Response;
    resp.ContentEncoding = System.Text.Encoding.GetEncoding("GB2312");
    resp.AppendHeader("Content-Disposition", "attachment;filename=" + fileName);
    string colHeaders = "", ls_item = "";

    ////定义表对象与行对象，同时用DataSet对其值进行初始化
    //DataTable dt = ds.Tables[0];
    DataRow[] myRow = dt.Select();//可以类似dt.Select("id>10")之形式达到数据筛选目的
    int i = 0;
    int cl = dt.Columns.Count;

    //取得数据表各列标题，各标题之间以t分割，最后一个列标题后加回车符
    for (i = 0; i < cl; i++)
    {
        if (i == (cl - 1))//最后一列，加n
        {
            colHeaders += dt.Columns[i].Caption.ToString() + "\n";
        }
        else
        {
            colHeaders += dt.Columns[i].Caption.ToString() + "\t";
        }

    }
    resp.Write(colHeaders);
    //向HTTP输出流中写入取得的数据信息

    //逐行处理数据 
    foreach (DataRow row in myRow)
    {
        //当前行数据写入HTTP输出流，并且置空ls_item以便下行数据   
        for (i = 0; i < cl; i++)
        {
            if (i == (cl - 1))//最后一列，加n
            {
                ls_item += row[i].ToString() + "\n";
            }
            else
            {
                ls_item += row[i].ToString() + "\t";
            }

        }
        resp.Write(ls_item);
        ls_item = "";

    }
    resp.End(); 
}

------解决方案--------------------
public static bool ExportToExcel(DataTable table, string excelName, int[] columnIndexs, string[] columnHeads)
   {
        Excel.ApplicationClass oExcel = new Excel.ApplicationClass();
       Excel.Workbook obook = null;
       Excel.Worksheet oSheet = null;
       Excel.Range range = null;
       #endregion
       try
       {
           obook = oExcel.Workbooks.Add("");
           oSheet = (Excel.Worksheet)obook.Worksheets[1];
           int rCount, cCount;
           rCount = table.Rows.Count;
           cCount = table.Columns.Count;
           object obj = System.Reflection.Missing.Value;

           if (cCount < columnIndexs.Length || cCount < columnHeads.Length)
           {
               throw new ArgumentOutOfRangeException("columnIndexs 与 columnHeads 长度必须一致。");
           }
           for (int i = 1; i <= columnIndexs.Length; i++)
           {
              
               range = (Excel.Range)oSheet.Columns.get_Item(i, obj);
               range.NumberFormatLocal = "@";
           }
           for (int c = 0; c < columnIndexs.Length; c++)
           {
               oSheet.Cells[1, c + 1] = columnHeads[c];
               for (int r = 1; r <= rCount; r++)
               {
                   oSheet.Cells[r + 1, c + 1] = table.Rows[r - 1][columnIndexs[c]].ToString();
               }
           }
           obook.SaveCopyAs(excelName);
          obook.Close(false, System.Reflection.Missing.Value, System.Reflection.Missing.Value);
           return true;
       }
       catch (Exception ex)
       {
           throw ex;
       }
       finally
       {
            ystem.Runtime.InteropServices.Marshal.ReleaseComObject(range);
           System.Runtime.InteropServices.Marshal.ReleaseComObject(oSheet);
           System.Runtime.InteropServices.Marshal.ReleaseComObject(obook);