Hi, I have got my S2 visa for 50 days, is it extendable and for how may days and the procedure?

Mujeeb, you can apply for an extension from local entry and exit management bureau at least 7 days before your current S2 expires. It requires your passport, temporary accommodation registration form, visa application form affixed with a passport photo in white ground and proof for your stay in China. For example, if you apply for S2 to stay with your families, then your family member's valid resident permit is required.

It usually takes 7 days to deal with your application. Theoretically, you can get as long as 180 days duration of stay. However, the bureau has the final say.