I got a double entry Business VISA for china but i can stay maximum for 28 days. i want longer stay

Hi, you can try to extend your current business M type in China. If it can be done, you don't need to go back to your home country.
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. Then submit the application to the exit and entry administration of the local PSB to apply for the extension.
You should extend it 7 days prior to its expiry date.