What should I do if the patent I applied for abroad is applied for by someone else after I return to China?

First check whether priority can be used. Within a certain period, the date of foreign application can be used. This period is 12 months.

If it exceeds 12 months, it can be resolved through negotiation or judicial channels. First obtain evidence and then file an infringement lawsuit in an intellectual property court.

Or sue the other party’s patent and determine it to be invalid; and then ask the other party to compensate for the losses.