The formation of an anal fistula is the inevitable result of the development of perianal abscesses, and the formation of an anal fistula roughly goes through four stages: the first stage: the infection and inflammation of the anal fossa and flap. The first stage is limited to local inflammation, which can spread around the anus if not treated in time. The second stage: Inflammation begins in the local anal fossa and flap and gradually spreads to form perianal rectitis. If the inflammation is not controlled, it may invade into the tissue interstices with low resistance to disease. The third stage: As the resistance of perianorectal tissues decreases, it becomes a place for germs to invade, spread, accumulate and multiply, making the tissues here prone to infection and inflammation, and the positive does not prevail over the evil, resulting in perianorectal abscess. If anorectal abscess can be handled properly in the early stage, it can often be dissipated and cured without leaving sequelae; if the early treatment time is delayed or improperly handled, the tissue necrosis and pus can spread along its local interstitial space, which will aggravate and complicate the condition, therefore, surgical incision and drainage should be performed as early as possible to drain the pus and control the inflammation development. The fourth stage: perianorectal abscesses break down on their own or after the incision and drainage of the change of treatment, although the abscess cavity gradually shrinks, but the ulcerated sore does not close the mouth for a long time, the cavity wall has formed a hard pipe wall of connective tissue hyperplasia, the gap left in the middle, which is the fistula, pus often flows out from the fistula, repeated infection, recurrent episodes, can not heal itself, and become a fistula.