Lower gastrointestinal bleeding is clinically subdivided into six major categories, which are inflammatory, mechanical, vascular, neoplastic, and systemic. Most of the lower gastrointestinal bleeding comes from the colon and rectum, and a few from the small intestine. The characteristics of their common diseases are briefly described as follows: 1. Colon and rectal polyps or colonic polyposis: intestinal polyps mostly occur in the rectum and sigmoid colon, most of them are single and a few are multiple. The main symptom is blood in the stool. Blood in stool is characterized by intermittent, bright red color, generally small amount, not mixed with feces. Children with blood in the stool, but the number and nature of the stool is basically normal, most of them are rectal polyps. Colon polyps are mostly seen in young adults, whose clinical features are diarrhea, fresh blood and mucus in the stool, which can cause anemia due to repeated bleeding. 2, colonic hemangioma: the main symptom is intestinal bleeding or intestinal obstruction. It can be manifested as acute hemorrhage, and anemia due to long-term small amount of blood loss is common. The hemangioma can be capillary hemangioma or cavernous hemangioma, or both. Colonoscopy reveals large extended veins under the mucosa. 3.Amoebic colitis: the patient has blood in the stool as the main symptom, and the stool is saucy red with mucus and foul odor, and there is often pressure pain in the right lower abdomen, and the urgency is less than that of bacillary dysentery. 4, rectal and colon cancer: rectal cancer blood in stool, bright red or dark red in early stage, not much, intermittent, often with alternating history of constipation and diarrhea; late stage stool often mixed with foul-smelling mucus at the same time. Left-sided colon cancer is similar to rectal cancer, but is prone to intestinal obstruction. Right-sided colon cancer has mainly tarry stools, and the stool occult blood test is often positive, accompanied by indigestion, anemia and right lower abdominal masses and other signs. 5.Diverticulitis of the colon: mostly located in the sigmoid colon, with habitual constipation. Asymptomatic diverticula without complications, such as inflammation of diverticula, there may be mucus and blood stool, abdominal pain, fever and other symptoms. 6, ulcerative colitis or other inflammatory diseases: large amount of blood in the stool is rare, often mucus blood stool, a history of diarrhea, abdominal pain, mostly accompanied by lower abdominal pain, colonoscopy and barium enema angiography can be clearly diagnosed. 7, internal hemorrhoids: the first and second stage of internal hemorrhoids are mainly blood in the stool, blood in the stool usually occurs during defecation, sometimes dripping, shooting blood, or only blood on the hand paper, blood and feces do not mix, bright red color. Stage III internal hemorrhoids are often accompanied by symptoms of hemorrhoid prolapse. The hemorrhoids bleed in small amounts, usually without urgency and pain, and often with constipation. 8, intestinal trap: often mucus and blood stool, jam-like, common in children, accompanied by abdominal pain, abdomen can be found in the lump of the trap, easy to cause intestinal obstruction. 9, Meniere’s diverticulum: also known as terminal ileal diverticulum, is a congenital disease, characterized by sudden blood in the stool, no abdominal pain or other symptoms, can be relieved by supportive therapy, but can soon bleed again. Bloody stools are often dark red with blood clots and cause shock and anemia when there is a lot of bleeding. For pediatric lower gastrointestinal bleeding of unknown cause, this disease should be thought of. 10.Small intestine tumor: benign tumor is rare, usually no systemic symptoms, and less bleeding. If the tumor is enlarged, it can cause black or red blood in the stool, often accompanied by abdominal distension, abdominal pain, loss of appetite, abdominal mass and other symptoms. 11.Anal fissure: bleeding during defecation, accompanied by anal pain, less bleeding, bright red, history of constipation, more common in young people, local examination can be seen in the anal canal fissure, mostly in the posterior middle or anterior middle. 12.Radioactive proctitis: blood in the stool, urgency, mixed blood and mucus, more frequent bowel movements, and experience of radiotherapy.