The pain in the middle of the left buttock can have the following causes: first, pear-shaped muscle syndrome, patients often have pain in the middle of the buttock at the pear-shaped muscle, serious cases can have the symptoms of sciatica in the lower limbs, this time to early physical examination, early nerve electromyography to diagnose and treat. Second, sciatic nodule bursitis, patients with sciatic nodule bursitis can have pain at the middle of the sciatic node of one side of the buttocks, and the pain is more obvious when sitting, so it is necessary to check the pelvic MRI and ultrasound at an early stage for early diagnosis and treatment. Third, tumor of bone, when there is a tumor or metastasis on one side of the sciatic bone, there can be pain in the middle of the buttocks on one side, then CT, ECT, MRI of the pelvis should be checked to diagnose and treat.