1, simple anal fistula: a, low simple anal fistula: there is only one fistula, a complete fistula with an internal and an external mouth. The inner mouth is at the dentate line and the tube passes through the external sphincter superficially or below the superficial part. b. High simple anal fistula: there is only one fistula, the inner mouth is at the dentate line or above the dentate line, and the tube travels above the deep layer of the external sphincter, or penetrates under the rectal mucosa without passing through the muscle (including internal blind fistula and total internal fistula). 2, complex anal fistula: 3, horseshoe-shaped anal fistula: fistula ring, the outer mouth on both sides of the anus, the inner mouth more in the truncated position at 6 or 12 points. There are also anterior, posterior and anterior-posterior horseshoe fistulas. a. Anterior horseshoe fistula: The fistula is circumferential, with the external opening in front of the anus spreading to the perineum and vaginal fistula on both sides. If the external opening is within 2 or 5 cm of the anal verge, the internal opening may be on the posterior side. b. Posterior horseshoe fistula: the fistula is circumferential, with the canal spreading to the posterior sides of the anus, farther and deeper from the anal verge. The path is complex.