The length of the rectum retained should not be too short The re-establishment of postoperative bowel function requires a coordinated muscular action and an intact neurological reflex system. Normal defecation and bowel control function depends on 3 basic conditions: i. Normal sphincter function of the anus. Second, complete defecation reflex function. Third, the storage function of feces. The defecation reflex is established by the volume and pressure generated by feces stimulating the intestinal canal receptors, the volumetric dilatation of the rectum stimulating the puborectalis muscle and pelvic floor muscles, and the uploading through the pelvic nerves causing the urge to defecate. The establishment of this reflex depends on the length of the recto-anal canal on the anal side, so the anal preservation surgery preserves at least the intact internal and external sphincter, the anal raphe, the anal canal and its innervated nerves. In order to maintain a normal number of bowel movements, the lower rectum should be preserved at 75px-100px. The longer the preserved rectum, the more intact the nerve reflex and the more ideal the defecation function. Ninety percent of patients have anal dysfunction after surgery There are objective and subjective indicators to judge the defecation function of postoperative patients. Objective indicators include: i. the function of the anal sphincter. ii. the length of the preserved rectum. The height of the anastomotic plane. Peripheral nerve injury or not. Subjective indicators include: I. Frequency of defecation. The randomness of defecation. The ability to distinguish between gas and stool. The degree of difficulty in defecation. After low and ultra-low anal preservation surgery, more than 90% of patients will have different degrees of anal dysfunction, which is known as anterior resection syndrome. Anterior resection syndrome is a syndrome consisting of a series of symptoms such as urgency of stool, frequency of stool and gas incontinence. A small number of patients may also present with constipation and difficult bowel movements. At the time of the current research table, anterior resection syndrome is associated with many factors, including anastomotic height, exogenous nerve injury, gastrointestinal tract reconstruction modality and preoperative adjuvant therapy. Of course, postoperative rehabilitation of bowel function is also very important, including exercising the storage function of the patient’s intestines, developing the habit of regular bowel movements, and adjusting the diet structure.