The validity period of the residence registration is normally
the same as the validity period of the visa (the validity period of
residence registration for foreigners whose country has mutual visa
exemption arrangement with china is usually one year).
If you cannot leave China before the validity of your residence
registration expires, you must request the entity you work for or
that hosts you to state to the Chinese visa authorities the reason
and length of extension in a note (official letter) attached with
valid passport at least three days before the expiry of your
residence registration for extension of your residence
registration.
(english.gov.cn)