This is a multicentre, randomized, double-blind, parallel, placebo-controlled Phase II clinical study of 261 adults with active ankylosing spondylitis to evaluate the efficacy and safety of JS005 in the treatment of active ankylosing spondylitis.

Inclusion Criteria:

1. Subjects voluntarily particpate in this clinical study and sign the informed consent form.
2. Male and female patients aged 18-75 years at the time of screening (both inclusive)
3. Meet the diagnosis of active Ankylosing Spondylitis(AS), have a record of radiological evidence consistent with the Modified New York Classification Criteria for ankylosing spondylitis as revised in 1984 4. Diagnosis of active AS (active AS is defined as: BASDAI >= 4, total back pain score >=4, and BASDAI second question spinal pain score >=4)

Exclusion Criteria:

1. Pregnant or lactating women.
2. Active diseases that may confound the evaluation of JS005: other autoimmune inflammatory diseases (including but not limited to systemic lupus erythematosus, rheumatoid arthritis, sarcoidosis, vasculitis, etc.) or chronic pain other than ankylosing spondylitis (including but not limited to fibromyalgia, osteoarthritis, etc.).

4. Active inflammatory bowel disease within 6 months prior to randomization. 5. Recurrent anterior uveitis or acute anterior uveitis within the last 4 weeks prior to randomization.

6. History or evidence of active or latent tuberculosis (TB), defined as a positive interferon gamma release assay (IGRA) or purified protein derivative (PPD) at the time of screening. 7. Positive hepatitis B virus test result 8. Prior exposure to JS005 or any other biologic that directly targets IL-17 or the IL-17 receptor.

9. use of >= 2 TNF-α inhibitors.