Cron job does not run, and have no logs

I want cron to run php artisan schedule:run for me every minute.This is what i do by now

1.I logged in with user root

2.I use service cron start to start cron service.

3.Then I use cron -e to add a new job * * * * * cd /var/www/html && php artisan schedule:run

4.Run service cron restart to restart the servcie.

5.And nothing happened. Job is not running, no logs, nothing.

6.Then I try to add a job * * * * * /bin/echo "cron works" >> /tmp/file, so now I have 2 jobs.The job * * * * * /bin/echo "cron works" >> /tmp/file works fine. but artisan command still not working.

7.So I think maybe artisan script have some problem while running, I run cd /var/www/html && php artisan schedule:run on the command line, and it works on the command line

8.Then I think maybe is the file permission problem, I run chmod +x /var/www/html/artisan. Still not working.

Here is my Kernel.php file:

    protected function schedule(Schedule $schedule){
        $schedule->call(function(){
            Log::debug('schedule is running');
        })->everyMinute();
    }

After five hours attempts, I finally give up. Which part did I do wrong.