i need to extend my f visa(just about 4 days). can you explain how can i get the extension?

You should first prepare the required documents which include your passport, the filled-out application form and a recent bareheaded color photo, valid registration form of temporary residence, an invitation letter from a unit in PRC, as well as the inviting unit’s relevant certifications, and relevant materials required by the exit and entry administration department. Afterwards, go to the exit and entry administration of the local PSB to apply for an extension.