1.What is anus-preserving surgery? For patients with low rectal cancer, anal preservation surgery has always been a hot topic of concern. The definition of anus-preserving surgery is: for patients with low rectal cancer who need to undergo Miles surgery according to the traditional classical surgery principles, a low or ultra-low anastomosis is performed with the help of the most advanced technology and instruments to preserve the original anal function (e.g. Dixon surgery, Parks surgery, etc.). Miles surgery is the last option in radical rectal cancer surgery. Its advantage is that the tumor is completely removed, but the disadvantage is that the anus must be removed and rerouted, and the patient’s postoperative quality of life is poor. However, the disadvantage is that the anus must be removed and rerouted, and the patient’s postoperative quality of life is poor. However, it must be soberly recognized that it is still crucial to correctly grasp the principles of anal preservation surgery and reasonably select the indications for it. On the contrary, Miles surgery should not be performed on the pretext of surgical completeness. The basic principles of anus-preserving surgery for low rectal cancer are: (1) to ensure the radicality of the tumor. Anal preservation surgery cannot affect the long-term survival rate after surgery and cannot increase the local recurrence rate after surgery. (2) Good postoperative anal defecation and control function, and improved quality of life. It is required to have sound sphincter function and complete sensory reflex function, otherwise the purpose of improving the quality of life is lost even if the anus is preserved. The closer the anastomosis is to the anal verge, the higher the incidence and more serious the degree of defecation dysfunction, manifesting as diarrhea, frequent stools, incontinence and other discomforts, which are related to the function of “new rectal capacity”. In order to improve the defecation function after super-low rectal anastomosis, colonic storage pouch or coloplasty can be attached if necessary, but the effect of storage pouch is more advantageous in the short term, but the long-term effect is not obvious. (3) The pelvic autonomic nerve should be preserved especially during anal preservation surgery to improve the urinary and sexual functions of patients and to improve the quality of postoperative survival. (4) If there is no cancer residue in the distal part of the intestinal canal, a certain length of normal intestinal canal above and below the primary cancer foci should be removed to ensure that the pathology of the distal cut edge is negative. (5) Strictly grasp the principle of individualized anus-preserving surgery and choose different anus-preserving surgery methods. If the residual rectum on the levator muscle is more than 2cm after rectal resection, Dixon operation is preferred; if the residual rectum is less than 2cm, trial anastomosis with double anastomosis is preferred with high success rate; if the residual rectum is too short and low level anastomosis is difficult, Parks operation or modified Bacon operation can be chosen. The indications for anal preservation surgery for low rectal cancer: whether anal preservation surgery can be performed for low rectal cancer mainly depends on the specific conditions of the patient and the surgeon. (1) Patient’s condition: whether the function of organs such as heart, lung, liver and kidney is normal, and whether they can tolerate surgery and anesthesia. (2) Tumor size, degree of differentiation, infiltrative metastasis and distance of the lower edge of the tumor from the dentate line. Preoperative evaluation should be done: rectal diagnosis to determine tumor site, size, shape, distance from dentate line, circumference and motility; intra-rectal ultrasonography to determine the depth of tumor infiltration; pelvic CT to determine circumference, depth of infiltration and relationship with other organs in progressive rectal cancer, and to observe whether there are enlarged lymph nodes in pelvis; MRI has high resolution for soft tissues and is more accurate in diagnosing parietal lymph nodes. The above methods can help to grasp the biological characteristics of rectal cancer, correctly determine the degree of tumor infiltration and progression, and combine with the specific intraoperative conditions to individualize and reasonably select the indications for anal preservation surgery. However, when the tumor infiltrates the anal sphincter and anal levator muscle, infiltrates the adjacent organs and causes pelvic fixation, or when the anal sphincter is dysfunctional before surgery, anal preservation surgery is not recommended. (3) The technical level of the surgeon and his team. This point is crucial and can play a decisive role in the success or failure of anal preservation.