1. Clinical manifestations: 1. Symptoms: recurrent episodes of perianal swelling and pain, pus flow, and fever during the acute inflammatory period. 2. Local examination: visual examination reveals depression or protrusion of the external opening with occasional discharge. The perianal area of shallow anal fistula can be palpated with hard cords, and its path can be judged. 3. Rectal palpation: depressions or hard nodes can be palpated near the dentate line, which can initially determine the location of the internal orifice; the function of the perianal sphincter can also be generally assessed. Ancillary examinations: 1. Probe examination: A silver ball-tipped probe is recommended for preliminary exploration of the fistula. Anorectal microscopy: Used in conjunction with hydrogen peroxide and low concentration methylene blue, it can determine or understand the location of the internal opening. 3, fistula x-ray imaging: using contrast agents such as pantopamine to inject the fistula from the external orifice, the canal alignment and the location of the internal orifice can be observed under dynamic, especially for the diagnosis of complex anal fistulae. 4. Endorectal ultrasound: to observe the course of the fistula, the internal opening and to determine the relationship between the fistula and the sphincter. However, it has some limitations and is mostly combined with clinical practice. 5.CT: It is used for the diagnosis of complex anal fistula, and can be performed simultaneously with the contrast examination. 6.Magnetic resonance imaging: It is the most objective diagnostic tool for complex anal fistula and the most accurate test for determining the efficacy. It can better show the relationship between fistula and sphincter with high accuracy, and should be promoted when available. 7.Anorectal pressure measurement: to understand and evaluate the function of anorectum.