This is a multi-center Phase 3 study to evaluate the safety and effectiveness of an investigational study drug (called Jaktinib) in adults (≥18 years and <65 years) who have 50% or greater scalp hair loss. The study is placebo-controlled, meaning that some patients entering the study will not receive active study drug but will receive tablets with no active ingredients (a placebo). It is double-blinded, meaning that the Sponsor, the study doctors, the staff, and the patients will not know whether a patient is on active study drug (or the dose) or placebo.

Inclusion Criteria:

• participants voluntarily sign the informed consent form (ICF);
• Age ≥ 18 years and <65 years, either male or female;
• Clinical presentation compatible with alopecia areata with a current episode lasting not exceeding ≤8 years.
• At least 50% scalp hair loss.
• Willing to comply with the study visits and requirements of the study protocol.

Exclusion Criteria:

• participants has taken a JAK inhibitor prior to randomization;
• participants who are unsuitable to the trial, as identified by the investigator.