Colorectal cancer is one of the major cancers affecting human health. Worldwide, its incidence rate, complication rate and death rate are on the rise. Currently, the incidence of colorectal cancer ranks second only to breast cancer. Recently, it has been reported that the mortality rate of colorectal cancer in China has increased by 4.71% annually. The incidence of colorectal cancer in China is 1.5-2 times that of colorectal cancer; ② mainly low rectal cancer is the most common; ③ the proportion of young people is as high as 15%. The main metastatic routes of colorectal cancer are: ① direct infiltration; ② lymphatic metastasis; ③ hematogenous metastasis; ④ implantation metastasis. Among them, lymphatic metastasis is the most important way of colorectal cancer metastasis. At present, a lot of clinical practice and research have confirmed that rectal cancer metastasis is mainly along the upper and lateral lymphatic drainage, and there are few lateral metastases for rectal cancer above the peritoneal fold, but there are lateral metastases for rectal cancer below the peritoneal fold. Only when the upper and lateral lymphatic drains are blocked by cancer cells or when cancer cells invade the dentate line, downward metastasis may occur, and its spread is extremely small, generally not more than 2.0 cm. Combining a large amount of literature from home and abroad, two points are basically clear: (1) the 3-year survival rate of low-grade rectal cancer that meets the indications for anus-preserving surgery will not be increased by performing Miles surgery; (2) the resection length of distal rectal cancer exceeds 50px, and the resection length of rectal cancer is already more than 50px. The resection length of more than 50 px is sufficient to basically achieve a negative distal margin. At the same time, physiological studies have shown that preserving the rectum and its mucosa 0.5-50px above the dentate line can basically preserve the complete defecation reflex arc and the satisfactory function of the anal sphincter. Therefore, the physiological and anatomical basis of anus-preserving surgery for low rectal cancer and its modern theoretical findings support it. The surgical methods of anal preservation for low rectal cancer At present, there are four types of anal preservation surgery for low rectal cancer: low anterior resection (LAR), rectal drag-out anastomosis (PISTA), local excision (LE) and intersphinceric resection (ISR). I. Transanal local excision Indications: Stage T1 tumor; invasion of less than 30% of bowel circumference; tumor diameter less than 75px; negative incision margin (>3mm from tumor); mobile or immobile; within 200px from anal margin; no vascular lymphatic infiltration or nerve infiltration; high or moderate differentiation; no imaging evidence of lymph node enlargement before treatment. Considering the risks of anesthesia and the high number of comorbidities and refusal of permanent artificial anostomy in elderly patients, the surgical options for LE are divided into transendoscopic surgery (TEM), transanal surgery, trans-sphincter surgery, and trans-caudal or sacral surgery. Advantages: are significantly lower surgical risks and postoperative complication rates; do not affect postoperative sexual function and urinary function; can avoid permanent bowel stoma; better postoperative anal bowel control compared with transabdominal low anterior resection, especially suitable for elderly frail patients with higher surgical risks or those who firmly refuse to have a permanent bowel stoma. Disadvantage: Even if full resection of local intestinal wall is performed, the lymph nodes metastasized around the intestinal wall and in the tumor drainage area within the mesentery cannot be resected together, so it can only be limited to early stage low to medium rectal cancer without lymph node metastasis. Indications: The lower edge of the mass is within 3-125px from the anal verge or 1.5-75px from the dentate line and does not infiltrate the external anal sphincter, puborectal muscle and anal levator muscle; good sphincter function; low rectal cancer at T1 and T2 stages, or low rectal cancer at T3 stage combined with neoadjuvant therapy; pelvic stenosis that prevents transabdominal completion of bowel resection. When intestinal anastomosis cannot be completed transabdominally due to stenosis. Advantages: not only can the anal sphincter be preserved to avoid permanent stoma, but also can obtain sufficient DRM and ensure the continuity of the intestine. At present, laparoscopic low rectal anus-preserving surgery is the most satisfactory procedure among all kinds of rectal cancer radical surgery in terms of curative effect and preservation of anal bowel control function. 1.Free abdominal incision colorectal resection via anal drag-out anastomosis is suitable for slow transmission constipation, sigmoid colon cancer, rectal cancer and other diseases. It has achieved more satisfactory results. The postoperative fecal function is satisfactory. No recurrence of the disease was seen in the short-term follow-up. For slow-transmission constipation, sigmoid colon cancer and medium-high rectal cancer, the transanal drag-out procedure was adopted; for low-grade rectal cancer (less than 7 cm from the anal verge), the transanal drag-out procedure with intestinal sleeve exenteration was adopted, which reduced the difficulty of operation and made the resection anastomosis more precise and lower. However, this procedure is not suitable for those with large tumors. However, this procedure is not suitable for those with large tumors, because the tumor is too large to be easily retracted through the anus. Advantages: It utilizes the natural cavity of human body, eliminates the abdominal incision, achieves higher degree of minimally invasive and cosmetic effect, and has no incision-related complications, and the operation is less traumatic and has quick recovery after surgery. 2.3D laparoscopic anterior rectal resection The clinical application of 3D laparoscopy makes the surgical anatomy more precise, and it has been possible to achieve white surgery with almost no bleeding, and anal preservation for ultra-low rectal cancer has become possible. It is suitable for rectal cancer without local infiltration 5-6 cm from the dentate line, and 3-4 cm of rectum and complete anal canal can be preserved after surgery, thus ensuring the functional integrity of the internal and external anal sphincter and anal levator muscle. Compared with traditional open surgery, there is no significant difference in postoperative complications, overall survival rate and disease-free survival rate between the two, but laparoscopy has a series of advantages such as less trauma, less intraoperative bleeding, shorter operation time and faster recovery.