I often have some patients call me and ask if they are suffering from anal fistula, I now summarize the common symptoms of anal fistula as follows for the reference of patients and friends to relieve their tension. The first thing you need to do is to get a good idea of what you are getting into. Because of the rapid growth of the external orifice, it often heals pseudo-chemically, resulting in repeated episodes of poor drainage and multiple fistulas and external orifices, and eventually becoming a complex anal fistula. The main symptom is the repeated discharge of small amounts of purulent, bloody, or mucus discharge from the external orifice of the fistula. In larger high anal fistulas, there is often fecal and gas discharge. Due to the stimulation of the discharge, the anal area is moist and itchy, sometimes forming eczema. When the external opening heals and the fistula is re-infected to form an abscess, it can be significantly painful and can be accompanied by systemic infection symptoms such as fever, chills, and malaise, which are relieved after the abscess breaks down or is incised and drained. Recurrent attacks of the above symptoms are the clinical characteristics of fistulas. The classification of anal fistulae varies according to different criteria, and the common classifications are: 1. classification according to the location of the fistula: fistulae are classified as low anal fistulae and high anal fistulae according to the location of the fistulae and the deep external sphincter. 2. divided into simple and complex anal fistulae according to the number of internal and external openings and the number of canals. Therefore, anal fistula can be divided into low simple anal fistula, low complex anal fistula, high simple anal fistula and high complex anal fistula. (1) Interanal sphincter type accounts for about 70% of anal fistulas and is mostly caused by perianal abscesses. The fistula is located between the internal and external sphincters, with the internal opening near the dentate line and the external opening mostly near the anal verge, and is a low anal fistula. (2) Transanal sphincter type About 25% of the fistulas are caused by abscesses in the sciatic anal canal space and can be low or high anal fistulas. The fistula passes through the external sphincter, the sciatic-rectal space, and opens on the perianal skin. （The fistula extends upward between the sphincters, crosses the puborectalis muscle, and penetrates the perianal skin through the colorectal space. (4) External anal sphincter is the least common, accounting for only 1%. It is mostly a consequence of a pelvic rectal gap abscess combined with a sciatic anal canal gap abscess. The fistulae are located from the perineal skin up through the scirorectal space and the anal raphe, and then penetrate into the pelvic cavity or rectum. These fistulas are often caused by trauma, intestinal malignancies, and Crohn’s disease and are more difficult to treat. In conclusion, the clinical symptoms of different types of anal fistulas may vary, but involving the impact of surgery on the morphology and function of the anus, it is more refined and scientific to classify fistulas according to their relationship with the sphincter muscle.