<?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//TRANSLIT', $data);

 echo $data;