Low rectal cancer surgery is divided into two categories according to whether the anus is preserved or not: non-anal preserving surgery is mainly the mile’s surgery and the columnar transabdominal perineal resection (Cylindrical APR), which has been improved in recent years; the other is various types of anus preserving surgery. (a) Combined perineal resection (APR) Combined perineal resection (mile’s procedure) is the classic surgery for low rectal cancer and is one of the most used procedures. And for tumors with more intense local infiltration recently Holm et al. adopted columnar transabdominal perineal resection. Mainly for patients with stage T3 and T4 low-grade rectal cancer, after freeing the upper rectal mesentery the mid-low rectal mesenteric resection is performed with the patient in prone position and distal rectal mesenteric resection through the perineum. The aim is to reduce the local recurrence rate by enlarging the resection through the perineum so that the specimen becomes cylindrical without stenosis of the lumbar region, increasing the amount of perineal tissue removed for distal rectal cancer and reducing the rate of positive CRM and intraoperative bowel perforation [14]. The study showed that postoperative complications and mortality did not increase significantly after columnar transabdominal perineal resection compared with conventional APR surgery, and it was superior to perineal operation with good visualization, and also reduced the risk of intraoperative operation to some extent. （Dixon’s surgery is another one of the most widely used clinically to preserve anus after mile’s surgery. The Dixon procedure is one of the most widely used anus-preserving procedures after the mile’s procedure. With the widespread use of anastomosis, the Dixon procedure has been expanded from being only applicable to tumors above the peritoneal fold to being applicable to low to mid-level rectal cancer surgery. 2.Modified Bacon procedure It was firstly proposed by Bacon in the 1940s, and later improved by Black as a method. The abdominal procedure is similar to the Dixon procedure, but the rectum is cut off 2-3 cm above the dentate line, and the specimen is removed and then the proximal colon is pulled out from the anal canal and left to heal naturally. 3, Welch operation In the 1950s and 1960s, a set of pull-out surgery was proposed, which is now collectively known as Welch operation. The basic procedure is: after freeing the rectum through the abdominal cavity, removing the lymph nodes and excising the diseased intestinal segment, the distal rectum is turned out of the anus through the anal canal, and then the proximal colon is pulled out from the turned out rectum to form a ligature. The turned-out rectal section is fixed with the pulled-out colon plasma membrane for several stitches, and is not anastomosed for a while, and then the excess pulled-out colon is cut off and anastomosed outside the anus in about 2 weeks, and then the anastomosis is returned to the pelvis. (3) Ultra-low (below 5cm from the anal verge) rectal cancer anus-preserving surgery 1.Mason’s surgery Traditional low rectal tumor resection via abdominal route is very difficult due to the narrow surgical site and deep surgical space and unclear field exposure. Mason’s operation has the advantages of direct access, superficial surgical site and spacious operation space. The operation method of Mason’s operation has been described in detail [15-18]. The key steps can be briefly described as follows: (1) Prone position under general anesthesia. (2) A median incision is made from 3-4 cm above the sacrococcygeal joint toward the anal verge. (3) Depending on the distance of the tumor from the anal verge, decide whether to remove the caudal bone or part of the sacrum. (4) After incising the anal sphincter and pelvic floor muscle, the posterior rectal wall is incised longitudinally. (5) Partial resection of the rectal wall or segmental resection of the rectum is performed according to the location, size and extent of the tumor involving the intestinal wall. (6) Anatomical repair of the pelvic floor muscles and all groups of anal sphincters. The procedure is particularly suitable for local excision of various rectal tumors 5-9 cm from the anal verge, such as early rectal cancer, rectal choriocarcinoma, early carcinoma of rectal choriocarcinoma, rectal carcinoid tumor, rectal mesenchymal tumor and other rectal adenoma, and is not limited by the orientation of the tumor in the rectum. It can ensure a safe margin for the tumor. Since the surgery is non-transabdominal and less invasive, it is suitable for palliative resection of rectal cancer patients who are elderly and frail and have serious contraindications to surgery. When this procedure is used to treat rectal malignancies, accurate preoperative evaluation of the disease is particularly important. In principle, only early-stage rectal cancer is indicated (except for palliative resection), so the depth and extent of lesion invasion should be determined by a combination of CT, MRI, intracavitary ultrasound, anal finger examination, etc., in order to provide comprehensive information to accurately grasp the indications for surgery. If there is an error in this assessment, such as postoperative pathological examination reveals that the tumor has invaded beyond the submucosa, then either radical transabdominal surgery for rectal cancer should be performed again, or postoperative chemoradiotherapy should be combined with close clinical follow-up to determine whether further surgical treatment is needed according to the change of the disease. The common complications after Mason’s surgery include wound infection and rectal skin fistula. Since the surgery is performed under the condition of rectotomy, it is very easy to cause contamination during the operation, so a good intestinal cleanliness can avoid postoperative wound infection to the greatest extent. If intraoperative contamination occurs, prophylactic antibiotics will effectively kill bacteria that have not yet multiplied, thus preventing possible postoperative wound infections. Intraoperative excision and suturing of the posterior rectal wall lesions should be performed with great care and caution, as most rectal skin fistulas occur in the posterior rectal wall. The incontinence of the anal sphincter after Mason’s operation is a serious complication, which may be related to the failure to repair the severed anal sphincter accurately at the end of the operation or to the severe wound infection after the operation, which may cause the original sutured sphincter to split. 2.Parks surgery In 1972, Parks proposed a new surgical method for low rectal cancer, in which the rectum was resected through the abdomen and the anus, and the colon and anus were anastomosed through the anus. In this method, 2 cm of the distal rectum was excised and 1:100,000 epinephrine saline solution was injected into the submucosa of the dentate line to make the submucosa float and separate the mucosa from the internal anal sphincter. The rectal mucosa of the anal canal is incised and stripped slightly above the dentate line with an electric knife to reach the upper edge of the internal sphincter, and the whole layer of the colonic section is intermittently sutured with the mucosa and muscle layer of the dentate line with absorbent sutures, and the rectum is cut off after meeting with the abdominal resection plane, and the anastomosis is located at the upper edge of the anal canal or the dentate line. 3, ISR surgery Transabdominal trans-inside and outside sphincter intermuscular proctocolectomy was originally introduced by Lyttle and Parks[19] , which was originally designed for the anal resection of patients requiring total colon and rectal resection due to inflammatory bowel disease, and the surgery only removes the internal sphincter of the rectoanal canal, preserving the external rectal sphincter and surrounding tissues, thus achieving the goal of avoiding long-term non-healing of the perineal incision. Since then, this procedure has been combined with the technique of colon2anal anastomosis and developed into a method of preserving the external anal sphincter, which is mainly used for the anal preservation treatment of low rectal cancer without invasion of the internal anal sphincter, low malignancy rectal tumors and benign rectal tumors, and also for the anal preservation treatment of rectal cancer in a slightly higher position with special pelvic stenosis. Surgery: The abdominal surgery for patients undergoing transcatheter internal and external sphincter resection is the same as the conventional free colon and rectum. The truncated position is taken and the operation follows the TME principle. Due to the low position of the tumor, it is necessary to cut the vessels at the root of the inferior mesenteric artery, and in case of tumor patients, the lymph nodes at the root of the mesentery can be cleared. The pelvic surgery team cuts down the sacro-rectal ligament and part of the levator muscle to reach the upper edge of the external anal sphincter ring, which corresponds to the level of the dentate line (recto-anal junction). In some thin patients, it is also possible to continue downward between the external sphincter ring and the wall of the intestinal canal (internal sphincter) for 1 to 2 cm. Surgery of the anal region is divided into total and partial resection of the internal sphincter, depending on whether the internal sphincter is completely removed. In cases of complete removal of the internal sphincter, the skin subcutaneous tissue is incised and the gap between the internal and external sphincter is found, and both muscles are wrapped by the muscle membrane. In cases of partial resection of the internal sphincter, the hypertrophied internal sphincter is cut vertically at the intended resection level to reach the internal and external sphincter gap and then sharply peeled proximally. The proximal dissection reaches the level of the dentate line, and then continues upward to the point where the levator muscle meets the internal sphincter to join the pelvic surgical group. The ISR procedure even has the potential to break through the 2-cm distal margin and has essentially the same results as the mile’s procedure, although, of course, the number of reported cases is not large and strict case selection should be emphasized. In addition, there are many recent reports of lumpectomy and robotic ISR surgery, which also represent an idea of future surgical exploration. 4. APPEAR surgery The ideal ultra-low level surgery should be able to completely eliminate the disease, allow colo-anal anastomosis to be performed safely under direct vision, and preserve the anal sphincter structure intact. A trans-anterior perineal ultra-low anterior rectal resection, referred to as the APPEAR procedure (Anterior Perineal PlanE for Ultra-low Anterior Resection of the Rectum, APPEAR), was recently invented by Professor Williams [27]. This procedure is divided transabdominally in the same way as a normal anterior resection, after separating the rectum to the level of the prostate, the perineum is incised from the anterior part through the perineal path, the pelvic floor muscle is dissociated under direct vision, and the perineum is operated above this plane of 2-3 cm at the extreme end of the rectum surrounded by the anal raphe; all the proposed cut colon and rectum are dragged out at the incision, the distal rectum is dissociated under direct vision, and the anastomosis is performed under direct vision. We were the first to perform 7 cases of APPEAR surgery in China, and our experience is that this procedure is similar to semi-mile’s: that is, after completing abdominal separation, before deciding to perform mile’s surgery, it is advisable to make an inverted “U”-shaped incision in the anterior perineum and perform anastomosis under direct vision. If the tumor does not invade the external sphincter, and if the rectum is separated under direct vision, the requirement of 2cm distal margin can be achieved. If this is not feasible, mile’s will be performed. this procedure broadens the scope of anal preservation surgery, and when combined with neoadjuvant therapy, it is believed that many cases that previously required anal resection can be preserved. The concept of ultra-low anastomosis anal preservation surgery and the scope of distal resection complete defecation function based on three factors: rectal fecal storage function, anorectal sensory function and anorectal ring sphincter function. Anal preservation is the preservation of the anal structures, i.e., the intact anorectal ring and the skin of the anal canal, in order to maintain a sound sphincter and sensory reflexes. The focal issue in performing ultra-low anastomosis for rectal cancer is how much of the normal intestinal canal and surrounding soft tissues need to be removed distal to the cancer. In the past, it was considered that at least 5 cm of the distal bowel should be removed, i.e., the “5 cm principle”. The 5 cm distal bowel resection for low rectal cancer often includes the anal canal, which has prompted scholars at home and abroad to conduct a lot of pathological and clinical randomized comparative studies on the pattern of retrograde infiltration and spread of rectal cancer. It is now clear that the lymphatic drainage of the rectum under the peritoneal reflex is upward and lateral, without downward spread; that resection of the distal bowel beyond 2 cm is sufficient for rectal cancer; and that the 5-year survival rate of low-grade rectal cancer eligible for anus-preserving surgery is not increased by Miles’ surgery. Patients with Dukes stage C who wish to preserve the anus should undergo preoperative or postoperative pelvic radiotherapy. Due to the anatomical limitations of the pelvis, it is often difficult to perform an ultra-low anastomosis in the deep pelvic floor, so the appropriate anastomosis should be selected according to the specific situation. Because of the size of the anastomosis and the closure device, it is difficult to anastomose the 1- to 2-cm-long rectal stump with the proximal colon even with a double anastomosis in patients with a small pelvis or obesity, and in this case, the Wechsler, Park’s or APPEAR procedures are preferred. Conclusion At the present stage of development of anorectal surgery, mile’s surgery is the appropriate and last choice for the selection of surgical approach for low rectal cancer. There are many options for anus-preserving surgery as long as the indications are well understood.