function str_split_unicode($str, $l = 0) {
if ($l > 0) {
$ret = array();
$len = mb_strlen($str, "UTF-8");
for ($i = 0; $i < $len; $i += $l) {
$ret[] = mb_substr($str, $i, $l, "UTF-8");
}
return $ret;
}
return preg_split("//u", $str, -1, PREG_SPLIT_NO_EMPTY);
}
$s = '中华人民abc共和\x01国'; 

print_r(str_split_unicode($s));
Array
(
    [0] => 中
    [1] => 华
    [2] => 人
    [3] => 民
    [4] => a
    [5] => b
    [6] => c
    [7] => 共
    [8] => 和
    [9] => \
    [10] => x
    [11] => 0
    [12] => 1
    [13] => 国
)