If from ming tombs to downtown of beijing, which subway I have to take?

You can take the subway Changping line to Xierqi, and then transfer to line 13 to the downtown area.

if i using subway, is it i have opportunity to visit friend yongsheng jade carving factory?

Yes, you can visit the factory after visiting the tombs. It is adjacent to Dingling Tomb. You can easily walk there within 20 minutes.
In addition, the suggested sightseeing time of the jade factory is about an hour. :)

Hi, Nick. The Ming Tombs metro station is still about 2.5 miles (4km) away from the scenic area. There is no shuttle bus available nowadays.
Thus you are suggested to take a bus no.314 from Changling Tomb or Dingling Tomb, get off at Changping Dongguan Station. Then transfer to subway Changping Line to go back to downtown area.