The normal perianal diameter of the anus is roughly 3cm in physiological state and up to about 6cm under anesthesia. The anus is the opening of the end of the digestive tract to the outside of the body. Due to the anal sphincter to control the opening and closing of the anus, usually closed tightly as an anterior-posterior longitudinal fissure, defecation expansion was rounded diameter of about 3 cm. After sacral anesthesia, the maximum diameter of the anus that can be reached by artificial dilatation is about 6 cm. Expansion of the anus is commonly used in the examination and treatment of anorectal diseases and postoperative recovery in the treatment, the patient should not operate privately, violent expansion, in order to avoid straining the normal tissues, or even complicate bleeding, perianal abscess, hemorrhoidal prolapse and so on. Daily life should pay attention to the health care of the anus, such as developing the habit of defecating once a day, controlling the time of defecation, avoiding prolonged squatting in the toilet, maintaining the cleanliness of the anus and eating more fiber-rich foods.