Multi-Entry visa with 12-month Validity

Dear Misses, Dear Mister,

I am a PhD-student at the university of Cologne and will be travelling to Guangzhou at the end of August in order to stay there for around 7-8 months. I wanted to apply for the Multi-Entry visum with 12-month Validity, but I am not sure whether I will have to leave the PRC every 90 days and come back on the same visum or if I have to apply for a new one each time. Could you maybe help me with this issue?

Thank you in advance.

Kind regards,
Manon Diederich