1, pus flow is the main symptom. The number of pus is related to the length of the fistula and how much it is. The new fistula has more pus flow and the secretions irritate the skin and make it itchy and uncomfortable. In larger high anal fistulas, because the fistula is located outside the sphincter, it is not controlled by the sphincter and often has fecal and gas discharge. Due to the stimulation of secretions, the anal area is moist and itchy, sometimes forming eczema. When the external opening is healed and an abscess is formed in the fistula, it can be painful and accompanied by fever, chills, malaise and other symptoms of systemic infection, and after the abscess is punctured or drained by incision. The symptoms are relieved after the abscess is punctured or drained. The recurrence of the above symptoms is the clinical characteristic of fistula. 2, pain: when the fistula is open without inflammation often does not feel pain, only localized swelling and discomfort, aggravated when walking. When the fistula is swollen and inflamed due to infection or poor drainage of pus, it can cause pain. In the case of internal fistula, you often feel burning discomfort in the lower part of the rectum and the anus, and pain when defecating. 3, itching: because the pus constantly stimulates the perianal skin, often feel itching, perianal dampness and discomfort, skin discoloration, epidermal peeling, fibrous tissue proliferation and thickening, and sometimes the formation of eczema. 4, poor defecation: complex anal fistula mouth for a long time, can cause the formation of large fibrotic scar or ring-shaped strips around the anorectum, affecting the anal diastole and closure, feel difficult when defecating, with the feeling of incomplete stool. 5, systemic symptoms: in the acute inflammatory phase and repeated attacks of complex anal fistula, fever of different degrees, or with long-term chronic wasting symptoms such as emaciation, anemia and weakness may appear. Most anal fistulas are caused by perirectal abscesses, so the internal mouth is mostly at the sinus on the dentate line, and the external mouth is formed at the place where the abscess breaks down or is cut and drained, and is located on the perianal skin. As the external opening grows faster, the abscess often heals pseudologically. The abscesses often heal pseudo-chemically, resulting in recurrent abscesses that break down or are incised, forming multiple fistulas and external openings, making simple anal fistulas complex. The pruritic canal is surrounded by dense fibrous tissue, with inflammatory granulation tissue near the lumen, and the lumen may become epithelialized in later stages. Tuberculosis, ulcerative colitis, Crohn’s disease, malignancy, and traumatic infection of the anal canal can also cause anal fistulae, but are less common.