The criteria for confirming the diagnosis of ankylosing spondylitis include the following: 1) the patient has recurrent low back pain, and the duration of stiffness and pain in the low back is more than three months; 2) functional activity limitation, mainly referring to the limitation of thoracic movement; 3) symptoms of pain in large joints; 4) imaging criteria mainly referring to the different x-ray grading of the sacroiliac joint. Among them, imaging abnormalities are the most important diagnostic criteria. Currently, the diagnostic criteria of the Spondyloarthritis Association are mainly for early-stage ankylosing spondylitis.