list($usec, $sec) = explode(" ", microtime());

$usec2msec = $usec * 1000;    //计算微秒部分的毫秒数(微秒部分并不是微秒,这部分的单位是秒)
$sec2msec = $sec * 1000;    //计算秒部分的毫秒数
$usec2msec2int = (int)$usec2msec;    //取整
$sec2msec2int = (int)$sec2msec;    //取整
$msec = $usec2msec2int + $sec2msec2int; //加起来就对了
var_dump($usec2msec, $sec2msec, $msec);