how does a common law partner of a foreigner who will obtain a work visa accompany him to China.

If your partner applies for the Z type one, then you should apply for S1 or S2 type if you want to accompany him in PRC. S1 enables to stay more than 180 days and you should remeber to change it to a resident permit when you arrive in PRC within 30 days. S2 type allows you to stay 180 days at most.