Sudden pain after 4 months of cesarean section wound may be caused by incision infection, endometriosis, scar formation and other reasons. 1. Incision infection: most cesarean section incisions can return to normal in about one month, but 4 months after cesarean section due to non-absorption of thread knot, trauma and other reasons, leading to cesarean section incision infection, resulting in redness, swelling, heat, pain and other symptoms of the incision. 2. Endometriosis: The endometrium of cesarean section spreads to the abdominal incision with the bloodstream, which can cause endometriosis in the abdominal incision, resulting in periodic pain and lumps in the incision. 3. Keloid formation: 4 months after cesarean section, scar formation at the wound, due to the physical condition, incision inflammation and other reasons lead to abnormal proliferation of local connective tissue at the incision, forming keloid, causing pain or itching at the incision. Sudden pain 4 months after cesarean section wound, timely consultation, under the guidance of the doctor to find out the situation, and give appropriate treatment.