Rectal cancer surgery is a malignant tumor surgery, therefore, complete resection of tumor, i.e., radical, is the primary goal, and anal preservation cannot be performed for the sake of anal preservation, which will lay the root of tumor recurrence; on the other hand, on the premise of radical, anal preservation surgery can not only improve patients’ postoperative quality of life, but also enhance their confidence in fighting against the disease. In addition to the direct influence of the distance between the lower edge of rectal tumor and anal edge, the anal preservation surgery for rectal cancer also needs to consider the biological characteristics of tumor (including general type, differentiation degree, growth mode, etc.), tumor orientation, infiltration depth, pelvic lymph node metastasis, patient’s obesity degree, pelvic cavity width and other factors, and decide according to the situation in surgery. Therefore, preoperative rectal examination, combined with endorectal ultrasound, pelvic CT, MRI and other examinations, and adequate assessment of the local infiltration and distant metastasis of the tumor are the prerequisites for performing anal preservation surgery. Generally speaking, in order to ensure the radical resection of tumor, the following prerequisites should be met for anal preservation surgery for rectal cancer: 1. the lower margin of tumor is >5.0cm from the anal margin (for some posterior rectal cancers, the tumor is about 3.0cm from the anal margin); 2. the tumor is more mobile in the rectal wall on rectal finger examination; 3. intracavitary ultrasound indicates that the tumor infiltration does not exceed the rectal plasma membrane layer; 4. CT or MRI shows that the tumor is 4.CT or MRI shows that the tumor is confined to the rectal wall or rectal mesentery, and there is no obvious metastasis in the pelvic lymph nodes; 5.Insurgical freezing of the distal margin of the tumor at least 1.0 cm does not show cancer infiltration; 6.Pelvic conditions allow the operation of intrapelvic anastomosis. For those who have the following conditions, combined abdominoperineal resection should be performed, which is also a contraindication to anal preservation surgery: 1. the tumor has involved the anal canal and has no gap with the sphincter muscle or has invaded the sphincter muscle; 2. the tumor has been fixed with the pelvic floor; 3. the tumor has invaded the surrounding tissues or organs according to intracavitary ultrasound or CT or MRI; 4. the peritoneal metastasis in the pelvic wall; 5. the distance between the distal incision and the sphincter muscle is <1,0cm; 6. the patient had original defecation insufficiency. For those who are evaluated for the first time as T3 or T4 stage rectal cancer and are not suitable for anal preservation surgery, neoadjuvant treatment can be performed, and then re-evaluation will be made to decide whether to perform anal preservation surgery according to the descending stage of the tumor.