The incidence of colorectal cancer is increasing and must be taken seriously, and one of the characteristics of rectal cancer in China is its low location, so improving the quality of survival on the basis of ensuring the radical effect is a real problem facing rectal cancer surgery in China. In the past, for tumors with lower edge < 5 cm from the anal edge, transabdominal perineal resect ion (APR) was routinely performed, which required removal of the anus and seriously affected the quality of life. In recent years, internal sphincter resection, also known as intersphincteric resect ion (ISR), has gradually gained attention. ISR is the extreme form of anus-preserving surgery for ultra-low rectal cancer, which requires partial or total removal of the internal sphincter to achieve the radical requirement, while preserving anal function. Therefore, for rectal cancers < 5 cm from the anal verge (lower margin of the tumor < 2 cm from the dentate line), partial or total resection of the internal sphincter is required to ensure radicality. Currently, the criteria for ISR are: tumor inferior margin < 5 cm from the anal verge (tumor inferior margin < 2 cm from the anorectal ring); local infiltration confined to the rectal wall or internal sphincter as determined by preoperative MRI; histological classification of high to moderate differentiation. The criteria for ISR are: invasion of the external sphincter; defecation dysfunction; stage T4 tumors are considered on a case-by-case basis; if the stage T4 tumor invades the posterior vaginal wall, ISR is feasible if only a portion of the posterior vaginal wall can be resected to achieve radical treatment; invasion of the superior anal canal is not a contraindication to ISR, and ISR is also feasible if the invasion is superficial and does not invade the external sphincter. The key points of ISR are as follows: Abdominal operation: In the lithotomy position, the rectum and its mesentery are freed to the level of the anal levator using the total mesorectal excision (TME) technique, and if necessary, the splenic flexure of the colon is freed to ensure a tension-free anastomosis between the sigmoid colon and the anal canal. The rectal canal is exposed on the pelvic floor, distal to the internal sphincter, and separated bluntly downward along the gap between the internal and external sphincters. The perineum is manipulated: a puller is placed below the interanal sphincter groove to fully expose the surgical field. To reduce bleeding, dilute norepinephrine (1:2,000,000) can be injected subcutaneously at the predetermined incision line below the dentate line. A circular incision is made along the intersphincteric sulcus to expose and dissect the internal sphincter and access the gap between the internal and external sphincters. Braun et al. reported a local recurrence rate of 11% and a 5-year survival rate of 62% for ISR. Rullier et al. performed ISR in 92 patients over 10 years with tumors 1.5-4.5 cm from the anal verge; the result was a local recurrence rate of 2% and a 5-year survival rate of 81%. The local recurrence rate was only 2% and the 5-year survival rate was 81%.