Difficulty in defecation in 3 years after low anal preservation surgery is mostly considered to be caused by nerve injury and anastomotic stenosis and other postoperative complications during the operation. 1. Nerve injury: low anal preservation surgery is mostly used in patients with rectal cancer, such as the tumor is far away from the anus, and the tumor cells can be considered when micro-infiltrating the perianal tissues. However, when the lymph nodes are cleared during operation, the peripheral nerves may be damaged, resulting in the symptom of difficult defecation. 2. Anastomotic stenosis: the anastomotic blood flow obstacle, infection and contracture will easily lead to narrowing of anal canal after wound healing, which will lead to the obstacle of feces passing in the intestinal lumen, and the symptoms of defecation obstruction will appear. If long-term defecation difficulties, it is recommended to go to the hospital in time, under the guidance of professional doctors to choose the appropriate treatment plan, to avoid aggravation of the condition.