In the early stages of ankylosing spondylitis in children, patients may experience low back pain or discomfort, pain or stiffness in the sacroiliac or knee joints. Ankylosing spondylitis is a chronic progressive inflammatory disease of the spine that occurs in young adults between the ages of 16 and 30 years old, often beginning in the sacroiliac joints and knee joints and gradually progressing upward to the spinal column resulting in ankylosis and deformity. In the early stage of ankylosing spondylitis in children, the disease starts from the large joints of the lower limbs, with lumbar pain, sacroiliac discomfort, and lumbar stiffness after getting up in the morning or when sitting or standing up for a long period of time, which is alleviated after activities. Symptoms worsen at rest, at rest, and resolve after activity. Half of the patients will first present with inflammation of the large joints of the lower limbs, such as the knee and sacroiliac. It is recommended that young people with the above symptoms should be alert to the possibility of ankylosing spondylitis, and should go to the hospital in time to improve the CT of sacroiliac joints, leukocyte antigen HLA-B27 and other tests, so as to make a clear diagnosis and then follow the doctor’s instructions for treatment.