Difficulty in defecation after anal preservation surgery for rectal cancer may be related to postoperative colonic anastomosis edema, nerve injury and normal phenomenon. 1. Postoperative colonic anastomosis edema: postoperative colonic anastomosis edema leads to localized narrowing of intestinal lumen, which causes obstruction of passage in the intestinal lumen, and then the symptom of difficulty in defecation will appear. 2. Nerve damage: when the lymph nodes are cleared during the operation, the nerves may be damaged, and the nerve damage may cause the symptoms of difficulty in urination and defecation. 3. Normal phenomenon: patients choose lighter fluid food in daily diet and do not eat food with coarse fiber or fat, which leads to less stool volume, and then the symptoms of difficulty in defecation will appear. Difficulty in defecation after anal preservation surgery for rectal cancer is recommended to seek medical treatment in time, so that the doctor can clarify the cause of the disease and treat it in time.