The difference between anal fistula and rectal cancer is quite big. Most of the anal fistulas are formed secondary to perianal abscesses, which usually have an external opening around the rectum, that is, a red and swollen area with pus flowing, and the smell of pus is rather foul. Rectal cancer usually manifests as bleeding in the stool, or an increase in the frequency of stool, thinning of the stool, or irregularity. If the location of rectal cancer tumor is low, rectal diagnosis can reach the lower edge of the tumor or even the whole tumor, if the location is high, rectal diagnosis is usually negative, and if necessary, it should be combined with colonoscopy for clarification.