The filing date of the design patent is 2021-1-01,so how do I fill in the validity period of my design patent?

The term of Article 42 of the Patent Law of People's Republic of China (PRC) is 20 years, the term of invention patent is 10 year, and the term of design patent is 15 year, all of which are counted from the date of filing. So your appearance patent is valid until 2036-11-01. Of course, don't forget to pay the annual fee.