The formation of an anal fistula is the inevitable result of the development of perianorectal abscesses, and the formation of an anal fistula goes through four stages: The first stage: Inflammation of the anal saphenous fossa and flap is limited to local inflammation, and if not treated in time, the inflammation can spread around the anus. The second stage: Inflammation begins in the local anal fossa and flap and gradually spreads to form perianal proctitis. If the inflammation is not controlled, it may invade the tissue spaces with low resistance to disease. The third stage: As the resistance of the perianorectal tissue gap decreases, it becomes a place for germs to invade, spread, accumulate and multiply, making the tissues here susceptible to infection and inflammation, and a perianorectal abscess is formed. If anorectal abscess can be handled properly in the early stage, it can often be dissipated and cured without leaving sequelae, but if early treatment is delayed or not handled properly, tissue necrosis and pus can spread along its local interstices, aggravating and complicating the condition. Therefore, surgical incision and drainage should be performed as early as possible to drain the pus and control the development of inflammation. The fourth stage: perianorectal abscess collapses on its own or after the incision and drainage for drug replacement, the pus cavity gradually shrinks, but the ulcerated sore does not close for a long time, the cavity wall has formed a hard pipe wall of connective tissue hyperplasia, the space left in the middle is the fistula, pus often flows from the fistula, repeated infection, recurrent episodes, after a long time does not heal itself, and become a fistula.