According to the relevant medical history, inflammatory spondylosis should be considered with the following manifestations: ① insidious appearance of low back discomfort; ② age <40 years; ③ persisting for more than 3 months; ④ stiffness in the early morning; ⑤ improvement of activity symptoms. With the above medical history, radiographs with signs of sacroiliac arthritis and HLA_B27 (X), the diagnosis of spondylosis is confirmed; further exclusion of psoriasis, inflammatory bowel disease or Reiter's syndrome arthritis, the diagnosis of primary AS can be made, rather than waiting until the spine is clearly ankylosed to make a definitive diagnosis. Commonly used clinical diagnostic criteria for AS are 1. lumbar spine is restricted in all three directions of forward flexion, lateral bending and backward elevation; 1. lumbar spine or low back pain or history of pain for more than 3 months; 2. restricted chest expansion, measured at the level of the 4th rib space, expansion ≤ 2.5 cm. According to the above clinical criteria and grading of sacroiliac arthritis x-ray changes. (1) Confirmed AS is: ① bilateral sacroiliitis grade III or IV with at least one of the above clinical criteria; ② unilateral sacroiliitis grade III or IV, or bilateral sacroiliitis grade II with clinical criteria item Ⅰ, or with clinical criteria item 2 item 3. (2) Suspected AS is: bilateral sacroiliac arthritis grade III or IV, but does not have any one of the clinical criteria.