<?php
header("Content-type:text/csv;charset=utf-8");
header("Content-Disposition:attachment;filename=aa.csv");
header('Cache-Control:must-revalidate,post-check=0,pre-check=0');
header('Expires:0');
header('Pragma:public');
$data = "\xEF\xBB\xBFaaaaa\tbbbbb\tccccc\n11111\t222222\t33333"; // \xEF\xBB\xBF是bom头
$data = iconv('utf-8', 'ucs-2', $data);
echo $data;

<?php
header("Content-type:text/csv;charset=utf-8");
header("Content-Disposition:attachment;filename=aa.csv");
header('Cache-Control:must-revalidate,post-check=0,pre-check=0');
header('Expires:0');
header('Pragma:public');
$data = "aaaaa,bbbbb,ccccc\n11111,222222,33333";
$data = iconv('utf-8', 'gbk', $data);
echo $data;