$re = '/(?:(?:###)?([^# \n]+))(?=$|(?:###[^# ]+)*[^\n]*?(http:\/\/[^\n]+))(?: http:\/\/[^\n]+)?/';
$str = 'a1@zjmainstay.cn###a2@zjmainstay.cn###a3@zjmainstay.cn http://www.zjmainstay.cn/my-regexp
a1@zjmainstay.cn###a2@zjmainstay.cn###a3@zjmainstay.cn###a4@zjmainstay.cn###a5@zjmainstay.cn http://www.zjmainstay.cn/deep-regexp';
$subst = "$1 $2\n";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php