1. Purulent sweat gland: mostly in the perianal area and subcutaneous buttocks, abscess shallow in and extensive lesions, thickening and hardening of the skin, acute small abscesses and chronic sinus tracts coexist, pus is thick and white powder porridge-like, with a special odor. The sinus tract is not connected to the anorectum. 2. Perianal folliculitis and boils: they occur in the caudal bone and perianal subcutis, the swelling is slightly protruding, there is pus spillage outside the mouth, and there are pus plugs in the outside mouth. Diagnostic lesions are not related to anorectum. 3. Anterior sacral teratoma: when accompanied by infection, it is similar to posterior rectal abscess. Anorectal palpation of the posterior rectal mass is smooth, without obvious tenderness, with cystic sensation. Mostly congenital, history should be pursued. x-ray shows presacral mass pushing rectum forward. There may be scattered calcified shadows. Pathologic examination can confirm the diagnosis. 4. Anorectal tumor: benign tumors are more limited, movable, with mild local symptoms, usually not ulcerated; malignant tumors are hard and solid, with ulcerated and uneven surface, often with pus and blood secretion, foul smell and filth.