解决方法如下所示：

findAll($sql);
//echo $result[1]['sn'];

//创建一个excel对象
$objPHPExcel = new PHPExcel();
// Set properties 

$objPHPExcel->getProperties()->setCreator("ctos")
    ->setLastModifiedBy("ctos")
    ->setTitle("Office 2007 XLSX Test Document")
    ->setSubject("Office 2007 XLSX Test Document")
    ->setDescription("Test document for Office 2007 XLSX, generated using PHP classes.")
    ->setKeywords("office 2007 openxml php")
    ->setCategory("Test result file");

//set width 
$objPHPExcel->getActiveSheet()->getColumnDimension('A')->setWidth(8);
$objPHPExcel->getActiveSheet()->getColumnDimension('B')->setWidth(10);
$objPHPExcel->getActiveSheet()->getColumnDimension('C')->setWidth(25);
$objPHPExcel->getActiveSheet()->getColumnDimension('D')->setWidth(12);
$objPHPExcel->getActiveSheet()->getColumnDimension('E')->setWidth(50);
$objPHPExcel->getActiveSheet()->getColumnDimension('F')->setWidth(10);
$objPHPExcel->getActiveSheet()->getColumnDimension('G')->setWidth(12);
$objPHPExcel->getActiveSheet()->getColumnDimension('H')->setWidth(12);
$objPHPExcel->getActiveSheet()->getColumnDimension('I')->setWidth(12);
$objPHPExcel->getActiveSheet()->getColumnDimension('J')->setWidth(30);

//设置行高度 
$objPHPExcel->getActiveSheet()->getRowDimension('1')->setRowHeight(22);

$objPHPExcel->getActiveSheet()->getRowDimension('2')->setRowHeight(20);

//set font size bold 
$objPHPExcel->getActiveSheet()->getDefaultStyle()->getFont()->setSize(10);
$objPHPExcel->getActiveSheet()->getStyle('A2:J2')->getFont()->setBold(true);

$objPHPExcel->getActiveSheet()->getStyle('A2:J2')->getAlignment()->setVertical(PHPExcel_Style_Alignment::VERTICAL_CENTER);
$objPHPExcel->getActiveSheet()->getStyle('A2:J2')->getBorders()->getAllBorders()->setBorderStyle(PHPExcel_Style_Border::BORDER_THIN);

//设置水平居中 
$objPHPExcel->getActiveSheet()->getStyle('A1')->getAlignment()->setHorizontal(PHPExcel_Style_Alignment::HORIZONTAL_LEFT);
$objPHPExcel->getActiveSheet()->getStyle('A')->getAlignment()->setHorizontal(PHPExcel_Style_Alignment::HORIZONTAL_CENTER);
$objPHPExcel->getActiveSheet()->getStyle('B')->getAlignment()->setHorizontal(PHPExcel_Style_Alignment::HORIZONTAL_CENTER);
$objPHPExcel->getActiveSheet()->getStyle('D')->getAlignment()->setHorizontal(PHPExcel_Style_Alignment::HORIZONTAL_CENTER);
$objPHPExcel->getActiveSheet()->getStyle('F')->getAlignment()->setHorizontal(PHPExcel_Style_Alignment::HORIZONTAL_CENTER);
$objPHPExcel->getActiveSheet()->getStyle('G')->getAlignment()->setHorizontal(PHPExcel_Style_Alignment::HORIZONTAL_CENTER);
$objPHPExcel->getActiveSheet()->getStyle('H')->getAlignment()->setHorizontal(PHPExcel_Style_Alignment::HORIZONTAL_CENTER);
$objPHPExcel->getActiveSheet()->getStyle('I')->getAlignment()->setHorizontal(PHPExcel_Style_Alignment::HORIZONTAL_CENTER);

// 
$objPHPExcel->getActiveSheet()->mergeCells('A1:J1');

// set table header content 
$objPHPExcel->setActiveSheetIndex(0)
    ->setCellValue('A1', '订单数据汇总 时间:' . date('Y-m-d H:i:s'))
    ->setCellValue('A2', '订单ID')
    ->setCellValue('B2', '下单人')
    ->setCellValue('C2', '客户名称')
    ->setCellValue('D2', '下单时间')
    ->setCellValue('E2', '需求机型')
    ->setCellValue('F2', '需求数量')
    ->setCellValue('G2', '需求交期')
    ->setCellValue('H2', '确认BOM料号')
    ->setCellValue('I2', 'PMC确认交期')
    ->setCellValue('J2', 'PMC交货备注');

// Miscellaneous glyphs, UTF-8 

for ($i = 0; $i < count($result) - 1; $i++) {
  $objPHPExcel->getActiveSheet(0)->setCellValue('A' . ($i + 3), $result[$i]['id']);
  $objPHPExcel->getActiveSheet(0)->setCellValue('B' . ($i + 3), $result[$i]['realname']);
  $objPHPExcel->getActiveSheet(0)->setCellValue('C' . ($i + 3), $result[$i]['customer_name']);
  $objPHPExcel->getActiveSheet(0)->setCellValue('D' . ($i + 3), $OrdersData[$i]['create_time']);
  $objPHPExcel->getActiveSheet(0)->setCellValue('E' . ($i + 3), $result[$i]['require_product']);
  $objPHPExcel->getActiveSheet(0)->setCellValue('F' . ($i + 3), $result[$i]['require_count']);
  $objPHPExcel->getActiveSheet(0)->setCellValue('G' . ($i + 3), $result[$i]['require_time']);
  $objPHPExcel->getActiveSheet(0)->setCellValue('H' . ($i + 3), $result[$i]['product_bom_encoding']);
  $objPHPExcel->getActiveSheet(0)->setCellValue('I' . ($i + 3), $result[$i]['delivery_time']);
  $objPHPExcel->getActiveSheet(0)->setCellValue('J' . ($i + 3), $result[$i]['delivery_memo']);
  $objPHPExcel->getActiveSheet()->getStyle('A' . ($i + 3) . ':J' . ($i + 3))->getAlignment()->setVertical(PHPExcel_Style_Alignment::VERTICAL_CENTER);
  $objPHPExcel->getActiveSheet()->getStyle('A' . ($i + 3) . ':J' . ($i + 3))->getBorders()->getAllBorders()->setBorderStyle(PHPExcel_Style_Border::BORDER_THIN);
  $objPHPExcel->getActiveSheet()->getRowDimension($i + 3)->setRowHeight(16);
}


// Rename sheet 
$objPHPExcel->getActiveSheet()->setTitle('订单汇总表');


// Set active sheet index to the first sheet, so Excel opens this as the first sheet 
$objPHPExcel->setActiveSheetIndex(0);


// Redirect output to a client's web browser (Excel5) 
ob_end_clean();//清除缓冲区,避免乱码
header('Content-Type: application/vnd.ms-excel');
header('Content-Disposition: attachment;filename="订单汇总表(' . date('Ymd-His') . ').xls"');
header('Cache-Control: max-age=0');

$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel5');
$objWriter->save('php://output');
?>

在header() 前面加上ob_end_clean() 函数，清除缓冲区, 这样就不会乱码了!