The first stage is the preliminary examination, and the period is about 3-6 months. After passing, the notice of first-instance qualification will be issued.
The second stage is substantive review, with a period of about 1-2 years (depending on the number of replies to review opinions). After passing the preliminary examination, you can formally enter the substantive examination stage by paying the substantive examination fee.
The third stage is the authorization stage, that is, your patent passes the substantive examination and issues a notice of authorization, and you can receive the invention patent certificate two months after you pay the authorization fee (certificate fee and annual fee).
Therefore, the whole application process (in the case that the patent has not been rejected) is between 1.5 -3 years.