Sacroiliac joint gap asymmetry can be caused by sacroiliac joint degeneration, local inflammation, bone tumor and other factors. 1. Degenerative changes of sacroiliac joint: degenerative changes of sacroiliac joint occur in old people, osteoporosis can occur, with obvious bone sclerosis and osteomalacia manifestation. When one side of the sacroiliac joint degeneration is serious, the joint space is narrowed severely, and bilateral sacroiliac joint space asymmetry can occur. 2. Local inflammation: Inflammation or tuberculosis of sacroiliac joint on one side, or unilateral involvement of sacroiliac joint by ankylosing spondylitis and other diseases can lead to the destruction of sacroiliac joint bone, which can be manifested as asymmetry of sacroiliac joint gap on both sides. 3. Bone tumor: when primary bone tumor occurs in one side of sacroiliac joint, or when other parts of the tumor metastasize to this area, invasion by the tumor can lead to destruction of bone, causing narrowing of the joint space, and bilateral asymmetry of the sacroiliac joint space will appear. When asymmetry of sacroiliac joint gap is found, one should consult doctor in time, and under the guidance of specialized doctors, appropriate treatment should be carried out actively, which will help the recovery of the disease.