public static function arr_split_zh($tempaddtext)
{
	$tempaddtext = iconv("UTF-8", "gb2312", $tempaddtext);
	$cind = 0;
	$arr_cont = [];

	for($i = 0; $i < strlen($tempaddtext); $i++){
		if (strlen(substr($tempaddtext, $cind, 1)) > 0){
			if (ord(substr($tempaddtext, $cind, 1)) < 0xA1){ //如果为英文则取1个字节
				array_push($arr_cont, substr($tempaddtext, $cind, 1));
				$cind++;
			}else{
				array_push($arr_cont, substr($tempaddtext, $cind, 2));
				$cind += 2;
			}
		}
	}
	foreach($arr_cont as &amp;$row){
		$row = iconv("gb2312", "UTF-8", $row);
	}

	return $arr_cont;
}

$array = self::arr_split_zh($content);
if (count($array) <= 54){
	return $content;
}else{
	$str = implode('', array_slice($array, 0, 54));
	return $str;
}

来源：博客园