This trial uses a multi-center, randomized, double-blind, placebo, parallel-controlled design, and it is expected that about 105 cases will be enrolled in about 10 sites.

The study is divided into two stages, the first stage (1-16 weeks) is the main study; the second stage (17-32 weeks) is the extended study. This study set up 3 groups:Jaktinib Hydrochloride Tablets 75mg Bid group, 100mg Bid group and a placebo control group. The subjects were randomly enrolled in the group 1:1:1.

Inclusion Criteria:

• Age 18-65, both gender;
• Active Ankylosing Spondylitis;
• Participants who have been treated with non-steroidal anti-inflammatory drugs(NSAIDs) and still have active disease, or Participants who are intolerant to NSAIDs and stop the drug;
• Participants receiving low-dose oral glucocorticoid therapy (≤10mg/d prednisone) should maintain a stable medication regimen for at least 4 weeks before the first dose of this study. Do not adjust the dose during the entire study period except in emergency situations.
• Participants receiving other non-prohibited co-drugs should maintain a stable medication regimen for at least 7 days before the first dose of this study;
• Understand and voluntarily signed informed consent.

Exclusion Criteria:

• A history of known or suspected complete spinal rigidity, or clinical and imaging confirmed complete spinal rigidity;
• A history of any other autoimmune rheumatic disease;
• Any history of joint prosthesis infection, and the prosthesis is still in place;
• Participants who are using strong opioid analgesics (such as methadone, hydromorphone, morphine, etc.);
• Participants who have been treated with any JAK inhibitors (such as Tofacitinib, Baricitinib, Ruxolitinib, Filgotinib, Upadacitinib, etc.);
• Participants who have drug abuse or alcohol dependence;
• Participants who have had herpes virus infection in the past month;
• Participants who have a history of venous thrombosis (regardless of current treatment);
• Any significant clinical and laboratory abnormalities that the investigator believes will affect the safety evaluator；
• Participants who cannot be treated and followed up according to the trial protocol;
• Any Participant considered by the investigator to be unsuitable to participate in this clinical study