收集了两种方法，一种是直接利用I/o读写去生成非标准格式的xls文件，速度很快。另外种就是直接使用EXCEL的COM组件实现，需要在项目中引用EXCEL的COM组件。

IO方法：

 public void exportFromDataTable(System.Data.DataTable dt, string pathName)
        {
            FileStream objFileStream;
            StreamWriter objStreamWriter;
            string strLine = " ";
            objFileStream = new FileStream(pathName, FileMode.OpenOrCreate, FileAccess.Write);
            objStreamWriter = new StreamWriter(objFileStream, System.Text.Encoding.Unicode);
            //循环写入列头名称
            for (int i = 0; i < dt.Columns.Count; i++)
            {
                 strLine = strLine + dt.Columns[i].ColumnName.ToString() + Convert.ToChar(9);
            }
            objStreamWriter.WriteLine(strLine);
            strLine = " ";
            //循环写入内容
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                strLine = strLine + (i + 1) + Convert.ToChar(9);
                for (int j = 1; j < dt.Columns.Count; j++)
                {
                    strLine = strLine + dt.Rows[i][j].ToString() + Convert.ToChar(9);
                }
                objStreamWriter.WriteLine(strLine);
                strLine = " ";
            }
            objStreamWriter.Close();
            objFileStream.Close();
        }

COM组件方法：

public void ExportToExcelByExcel(System.Data.DataTable dt, string pathName)
        {
            object objOpt = System.Reflection.Missing.Value;
            Excel.Application excel = new Excel.Application();
            excel.Visible = true;
            Workbook wkb = excel.Workbooks.Add(objOpt);
            Worksheet wks = (Worksheet)wkb.ActiveSheet;
            wks.Visible = XlSheetVisibility.xlSheetVisible;
            int rowIndex = 1;
            int colIndex = 0;
            System.Data.DataTable table = dt;
            foreach (DataColumn col in table.Columns)
            {
                colIndex++;
                excel.Cells[1, colIndex] = col.ColumnName;
            }

            foreach (DataRow row in table.Rows)
            {
                rowIndex++;
                colIndex = 0;
                foreach (DataColumn col in table.Columns)
                {
                    colIndex++;
                    excel.Cells[rowIndex, colIndex] = row[col.ColumnName].ToString();
                }
            }
            try
            {
                wkb.SaveAs(pathName, objOpt, null, null, false, false, XlSaveAsAccessMode.xlNoChange, ConflictOption.OverwriteChanges, null, null, null, null);
            }
            catch (Exception ex)
            {
                throw new Exception(ex.Message);
            }
            finally
            {
                wkb.Close(false, objOpt, objOpt);
                excel.Quit();
            }
        }

引用3个DLL：Interop.Excel.dll，Interop.VBIDE.dll，Interop.Office.dll（下载地址见下）

在项目中：using Excel;

下载：ExportToExcelDLL.7z

调用示例方法如下：

　　　　　　  if (saveFileDialog1.ShowDialog() == DialogResult.OK)
                {
                    ExportToExcel excel = new ExportToExcel();
                    excel.exportFromDataTable((DataTable)dataGridViewX1.DataSource, saveFileDialog1.FileName);
                    MessageBox.Show("成功");
                }