以下是我编写的代码，实现对中英文混杂字符进行分割：

<?php
function mbStrSplit ($string, $len=1) {
    $start = 0;
    $strlen = mb_strlen($string);
    while ($strlen) {
        $array[] = mb_substr($string,$start,$len,"utf8");
        $string = mb_substr($string, $len, $strlen,"utf8");
        $strlen = mb_strlen($string);
    }
    return $array;
}

header('Content-type:text/html;charset=utf-8');
$str = '我爱北京3我爱上海-我爱xianggang';
$r = mbStrSplit($str, 4);
echo '<pre>';
print_r($r);
echo '</pre>';
?>

运行结果：

Array
(
    [0] => 我爱北京
    [1] => 3我爱上
    [2] => 海-我爱
    [3] => xian
    [4] => ggan
    [5] => g
)