The goal of this clinical trial is to To evaluate the efficacy of subcutaneous (SC) Netakimab in adult Chinese patients with Active Ankylosing Spondylitis. Researchers will compare Netakimab to placebo to see if Netakimab works to treat Ankylosing Spondylitis.

Inclusion Criteria:

1. Patients fully understand the objectives, procedures and possible adverse reactions of this study, voluntarily participate in the study and sign the informed consent form (ICF) approved by the Institutional Ethics Committee (IEC).
2. Male or female aged 18-65 years (inclusive) on the day of signing the ICF.
3. Patients meet the diagnostic criteria for ankylosing spondylitis (New York criteria as modified in 1984) and have a history of back pain for ≥ 3 months, with onset age < 45 years.
4. BASDAI score ≥ 4 at screening and baseline, and a spinal pain score [using a 0-10-point numerical rating scale (NRS)] of ≥ 4.
5. Suboptimal or no response to NSAIDs.
6. For patients taking NSAIDs regularly as treatment for ankylosing spondylitis, a stable dose of at least 2 weeks is required to be maintained prior to randomization.
7. At screening, if patients have received or are receiving a TNF-α inhibitor (not more than 1), the duration of administration must be no less than 3 months (at an approved dose) and the patients have a poor efficacy or are intolerant of the TNF-α inhibitor.
8. Female patients should have a negative blood pregnancy test.

Exclusion Criteria:

1. Complete ankylosis of spine joint with syndesmophyte on the cervical vertebra, thoracic vertebra, and lumbar vertebra sides of all intervertebral spaces.
2. Patients who are known to be allergic to any component of the investigational product or other excipients.
3. Prior use of any monoclonal antibody targeting interleukin 17 (IL-17) or interleukin 17 receptor (IL-17R), IL-12/23, or any other monoclonal antibodies for the treatment of ankylosing spondylitis (except for antibodies targeting TNFα)
4. Current or previous tuberculosis (TB) infection or latent TB
5. History of lymphoproliferative disorders such as lymphoma, or current signs and symptoms suggestive of lymphoproliferative disorders.
6. Any active malignancy or history of malignancy (with the exception of squamous carcinoma in situ or basal cell carcinoma of the skin or cervical cancer in situ with curative outcome) within 5 years prior to screening.
7. Major surgery (including joint surgery) within 3 months prior to screening, or surgery planned during the study.
8. Patients who have the following active infections or history of infections:
9. Presence of hepatitis B [hepatitis B surface antigen positive (HBsAg +), or anti-hepatitis B core antibody positive (HBcAb +) and HBV DNA positive], hepatitis C [hepatitis C antibody (anti-HCV Ab) positive and HCV-RNA positive], human immunodeficiency virus (HIV), or syphilis infection.
10. A history of epileptic seizure or convulsion.
11. Chronic intestinal inflammatory disease (except 'rohn's disease, nonspecific ulcerative colitis).