With the continuous development and maturity of low rectal anastomosis technology and the determination of the principle of safe incision margin of 2 cm distal to the tumor, low rectal cancer whose lower margin is 2 cm or more from the dentate line or 4 cm or more from the anal margin, and which does not invade the anal sphincter and anal levator muscle, is suitable for radical anus-preserving surgery. For highly malignant tumors such as mucinous adenocarcinoma, the length of distal bowel resection should be 5 cm, and the lower edge of the tumor should be 5 cm or more from the dentate line or 7 cm from the anal verge before anus-preserving surgery is performed.