i want to apply for a visiting visa,and visit my my sister at a university in wenzhou

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 sister, your sister's passport and Chinese residence permit and the copies. Then, go the China embassy to submit the application.
After your entry and if you want to stay longer, you can go to the exit and entry administration of the local PSB to apply for the extension. You can extend it 7 days prior to its expiry date.