The difference between sacroiliac arthritis and ankylosing spondylitis is mainly from the following aspects: first, sacroiliac arthritis is not necessarily ankylosing spondylitis; second, the onset of ankylosing spondylitis usually starts from the sacroiliac joints, so ankylosing spondylitis may be the reason for the occurrence of sacroiliac arthritis; third, sacroiliac arthritis may be caused by viral infections or bacterial infections, but ankylosing spondylitis is usually an autologous Third, sacroiliitis may be caused by viral infection or bacterial infection, but ankylosing spondylitis is generally an autoimmune disease, which is not related to bacterial infection. Fourth, the symptoms of sacroiliitis are mainly obvious around the sacroiliac joints, while ankylosing spondylitis will gradually extend to the surrounding joints, such as lumbar vertebrae joints or hip joints, and cause the corresponding symptoms.