Under Chinese law, a foreign national who overstays his/her visa in China is subject to fine and other penalties.
Need to stay longer? You must be obtain approval from a local public security authority, above county level, thirty (30) days before the duration of stay expires. You will be permitted to stay in China once the application is approved.
If you have been issued a visa in the past, the validity of the visa needs to be checked. If the visa is already expired or the entries are used up, you should apply for a new visa. Please check the visa you have been issued in the past. It could still meet the need for your trip.