An anal fistula is a granulomatous duct that connects the anal canal or rectum to the perianal skin and consists of three parts: an internal opening, a fistula, and an external opening. The internal port is located in the rectum or anal canal and is mostly one; the external port is in the perianal skin and can be one or more. It is characterized by long-lasting and repeated intermittent episodes. Most of them are caused by perirectal abscesses, and the internal orifice is located at the sinus on the dentate line, and the external orifice is formed when the abscess breaks down by itself or when the incision is drained. The classification of anal fistula: 1) low anal fistula: the fistula is located below the deep external sphincter; 2) high anal fistula: the fistula is located above the deep external sphincter. 2. According to the relationship between the fistula and the sphincter muscle, the fistula is divided into: ① inter-anal sphincter muscle type: this type is the most common, accounting for 70%. The fistula is located between the internal and external sphincter of the anus, and the external mouth is near the anal verge, which is a low anal fistula. The fistula is superior to the puborectalis muscle and then penetrates the perianal skin through the sciorectal space; ④ extra-anal sphincter type: at least one percent, often caused by trauma and malignant Crohn’s disease, which is difficult to treat. Clinical manifestations of anal fistula: The main manifestations are small amounts of purulent, bloody, and mucus-rich material coming from the external mouth, and fecal and gas discharge from larger high fistulas. When pus accumulates in the fistula, it can be painful and accompanied by fever, chills, and weakness, and the symptoms are relieved when the abscess breaks down or is drained. Recurrent symptoms are characteristic, and physical examination reveals one or more external openings in the perianal skin, with red papillary elevations and pus or purulent discharge when squeezed. The greater the number of external openings and the more distant from the anal verge, the more complex and difficult the fistula is to treat. Surgical treatment of fistulas: The vast majority of fistulas require surgical treatment, which is based on the principle that the fistula is incised to create an open wound to facilitate healing. The key to surgery is to minimize damage to the anal sphincter, prevent anal incontinence, and avoid recurrence. 1. Fistulotomy: for low anal fistulas. 2.Wire treatment: It is suitable for high simple anal fistula with internal and external openings within 3-5 cm from the anal verge, or as an adjunctive treatment for complex anal fistula. The biggest advantage: it is not easy to cause anal incontinence. This method is easy to operate, less bleeding and convenient to change medication. 3.Anal fistula excision: applicable to low simple anal fistula.