Extension of Multiple Entry Visa M

Hi, that's possible to extend that within China. You can apply for an extension 7 days before your each stay period expires, but the extended time won't exceed the original duration of stay.
You should first prepare your passport, valid registration form of temporary residence, the application form, a passport-style photo, and an invitation letter from your business partner, as well as the return ticket.
And then submit the application to the exit and entry administration of the local PSB to apply for the extension.