/**
 * 将一个字符串转换成数组，支持中文
 * @param string    $string   待转换成数组的字符串
 * @return string   转换后的数组
 */
function strToArray($string) {
    $strlen = mb_strlen($string);
    while ($strlen) {
        $array[] = mb_substr($string, 0, 1, "utf8");
        $string = mb_substr($string, 1, $strlen, "utf8");
        $strlen = mb_strlen($string);
    }
    return $array;
}

$string = '这里就是要转换成数组的字符串，www.liqingbo.cn';
$arr = strToArray($string);
print_r($arr);

Array
(
    [0] => 这
    [1] => 里
    [2] => 就
    [3] => 是
    [4] => 要
    [5] => 转
    [6] => 换
    [7] => 成
    [8] => 数
    [9] => 组
    [10] => 的
    [11] => 字
    [12] => 符
    [13] => 串
    [14] => ，
    [15] => w
    [16] => w
    [17] => w
    [18] => .
    [19] => l
    [20] => i
    [21] => q
    [22] => i
    [23] => n
    [24] => g
    [25] => b
    [26] => o
    [27] => .
    [28] => c
    [29] => n
)