<?php

$content = "xxxxx"; //你的内容

$result = preg_replace("/T.*Z/i","",$content);

echo $result;

用PHP处理小文件可以，文件大了还是用sed比较快
sed -i "s/T.*Z//g" test.txt

如果用正则匹配的话，可能注册的用户名中也有TZ字符，所以可以考虑字符串截取 毕竟T17:15:08Z,2016-06-16这一段的长度是固定的

用正则

$subject = '6691.club,已经注册,2015-06-17T17:15:08Z,2016-06-16';
$pattern = '/(.*,[\d]{4}-[\d]{2}-[\d]{2})T[\d:]{8}Z(,[\d]{4}-[\d]{2}-[\d]{2}$)/';
preg_match($pattern, $subject, $matches);
print_r($matches);
/*
Array
(
[0] => 6691.club,已经注册,2015-06-17T17:15:08Z,2016-06-16
[1] => 6691.club,已经注册,2015-06-17
[2] => ,2016-06-16
)
*/

$result = preg_replace("/T\d{2}:\d{2}:\d{2}Z/", " ", $str);

$str 是你的文本

谢谢各位，通过学习楼上诸位的代码,我自己学习加工了下：
全段代码如下：

<?php
$handle  = @fopen ("4.txt","r" );
if ( $handle ) {
    while (( $buffer  =  fgets ($handle ,4096 )) !==  false ) {
       // echo  $buffer."<br>\n";
        echo preg_replace('/\w\d\d\:\d\d\:\d\d\w/',"",$buffer)."<br>\n";
    }
    if (! feof ( $handle )) {
        echo  "Error: unexpected fgets() fail\n" ;
    }
     fclose ( $handle );
}
 ?> 

基本上达到我要的目的了，再次感谢楼上各位的帮忙