The fistula is characterized by a fistula with an internal opening located in the anal sinus, a tube passing through the perianal and rectal tissues, and an external opening located in the perianal skin, often with purulent secretions flowing from the external opening, causing local swelling and pain whenever the external opening closes. Swelling and pain; and then re-rupture of pus at or near the original external mouth, so repeatedly, and the reasons for its difficulty in healing are as follows: 1, the internal mouth and the primary foci of infection continue to exist, although the abscess is incised and drained, but the primary foci of infection anal cryptitis, anal gland infection still exists, intestinal contents can also continue to enter from the internal mouth. 2, because the intestinal cavity of feces, intestinal fluid and gas continue to enter the fistula, the formation of long-term chronic inflammation and repeated infection, so that the wall of the connective tissue hyperplasia thickened, the formation of fibrotic wall, the wall is difficult to close, and the tube is often bent narrow, so that the drainage is not smooth. 3, the fistula is at different heights through the anal sphincter, local inflammatory stimulation and other factors can cause spasm of the anal sphincter, which prevents the drainage of pus in the lumen and adversely affects the healing of the fistula. 4, the external mouth is narrow, sometimes closed, poor drainage of the pus cavity, pus accumulation can lead to abscess recurrence and penetrate the skin to form a new branch.