Suddenly there is a large amount of fresh blood coming out from anus, mainly consider the following reasons. First, considering colorectal tumor, the cancerous tissue invades large blood vessels and the surface mucosa is fragile in the late stage of tumor. When the patient defecates, especially when constipation, the stool is coarse and hard, and when the patient exerts himself to discharge it, it may cause the blood vessels to rupture and bleed profusely, and the color of the blood is bright red. Second, consider ulcerative colitis, the patient due to segmental mucosal erosion, ulceration bleeding, and in severe cases may cause perforation, so it may cause a large amount of blood flow. Third, consider having internal hemorrhoid bleeding, early internal hemorrhoid due to the surface mucosa did not form fibrous tissue. When constipation occurs or the patient is on fire when the surface mucosa rupture, easy to occur a large amount of bleeding. When there is a large amount of bleeding if not able to stop bleeding in a short period of time, need to be hospitalized as soon as possible, it is recommended that the anorectal department to do emergency treatment.