百度出來的無法使用，只好自己寫，有bug的地方歡迎留言，感謝

function from62to10($str){
    $dict = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $len = strlen($str);
    $dec = 0;
    for($i = 0;$i<$len;$i++){
        //找到對應字典的下標
        $pos = strpos($dict, $str[$i]);
        $dec += $pos*pow(62,$len-$i-1);
    }
    return $dec;
}

echo from62to10('6r2HqO');
echo '<br>';

$dec = '5896401674';
function from10to62($dec) {
    $dict = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $result = ''; 
    do {  
        $result = $dict[$dec % 62] . $result;  
        $dec = intval($dec / 62);  
    } while ($dec != 0);  
    return $result;
}

echo from10to62($dec);