after installed php by $ sudo apt install php, we can check the php version by $php -v, to me ,it is 7.0.
so in order to connect to mysql in $php -S localhost:80000, we need to install mysql extension or the program can`t connect to mysql.
$sudo apt install php7.0-mysql
so ,that`s ok, now we can run wordpress through $php -S localhost:8000