How do I know the expiration date of someone else's patent?

On China National Intellectual Property Administration's website or soopat, carry out patent search, find the patent, and check the legal status and application date.

Legal status refers to whether it is effective at present.

The limitation of utility model and design is 10 year from the date of application, and the invention is 20 years.

However, it should be noted that the invention will be in a "trial" state, which does not mean that it is valid or invalid, but only means that someone else has applied, and the application has been made public and is under review (generally speaking, it is valid if it is approved, and invalid if it is not approved).