Anal fistula, also known as anal leakage, is the abbreviation for anorectal fistula. Anal fistula is named after the morphology of its onset. This is because the main symptom is the repeated flow of pus or pus and blood from the sore on the skin around the anus, and even the flow of feces, which is why it is called a leak. The folk name for this disease is based on its symptoms, and it is commonly referred to as “fecal rat” because of the image of a fecal rat hiding in the sore. An anal fistula is a granulomatous canal around the anus, consisting of an internal port, a fistula, and an external port. It is a common rectal and anal canal disease that can develop at any age, accounting for 20% to 30% of all anorectal cases, mostly in young and middle-aged men. Most fistulas are caused by perirectal abscesses, so the internal opening is mostly at the sinus on the dentate line, and the external opening is formed at the place where the abscess breaks down by itself or is incised and drained, and is located on the perianal skin. The Western medicine believes that anal fistula is the sequelae of perirectal abscess, the causes of which are mainly the following: 1, perirectal abscess: is the most important cause of the formation of anal fistula, more than 95% of anal fistula are caused by the contamination of feces retained in the anal fossa caused by anal adenitis. 2, rectal anal injury: caused by trauma, swallowing bones, metal, anal thermometer, anoscopy and other damage to the rectum of the anal canal, bacteria invade the wound. 3.Anal fissure: repeated infection can be complicated by subcutaneous fistula. 4, perineal surgery: infection after internal hemorrhoid injection into the muscular layer by mistake or surgery, infection after postpartum perineal suture, infection after prostate and urethra surgery, etc., can spread to the anorectum causing abscess and fistula. 5, tuberculosis: in the past, tuberculosis complicates the tuberculous anal fistula is very much, up to 26.9%. In recent years there has been a significant decline, mainly caused by swallowing tuberculosis bacteria, a few can also be caused by bloodstream infection. 6, ulcerative colitis: Britain and the United States reported that 8.4% to 13.0% of people with anal fistula, Japan is about 15.4%. 7, Crohn’s disease: with anal fistula up to 14% ~ 76%. 8, rectal and anal canal cancer: the deeper part is often complicated by anal fistula. 9, bloodstream infection: diabetes, leukemia, aplastic anemia and other diseases, due to the body’s resistance to reduce the bloodstream infection often caused by anal fistula. The Chinese medicine believes that the formation of anal fistula is mostly due to improper treatment of perianal abscesses after breaking down, residual toxicity is not exhausted, and the blood flow is not smooth or due to external sensation of wind, heat, dryness, fire, dampness and excessive consumption of fat and sweetness causing deficiency of both lung and spleen.