The author’s experience: among the patients with blood in stool seen in outpatient clinics every year, a significant proportion of them visit the hospital because of blood in stool and are eventually diagnosed with bowel cancer through colonoscopy, and some of them are around 50 years old and are found to be at an advanced stage, which is very regrettable. Therefore, the author suggests that patients aged >45 with more than three episodes of blood in the stool should go to hospital for consultation and treatment, and if necessary, undergo colonoscopy to exclude intestinal cancer; if possible, people aged >45 should develop the awareness of performing anal finger examination or colonoscopy during regular medical checkups, regardless of whether they have blood in the stool or not. Early detection and treatment should be achieved. Blood in the stool is usually seen in the lower gastrointestinal tract, especially in the colon and rectum, but occasionally in the upper gastrointestinal tract. Blood discharged from the anus, blood in the stool, or all blood in the stool, bright red, dark red or tarry in color, are all called blood in the stool. So, what are the common causes of blood in stool? Specifically, it can be divided into the following two main types of blood in the stool: 1, painless blood in the stool 1, intestinal polyps: less bleeding, bright red blood, and the stool does not mix, sometimes with mucus, polyps near the anus can sometimes prolapse outside the anus. 2, hemorrhoids: mainly internal hemorrhoids blood in the stool, blood in the stool usually occurs during or after defecation, in the form of dripping or spraying blood, bright red blood, not mixed with stool, occasionally accompanied by swelling prolapse. 3, intestinal malignant change: manifested as an increase in the number of stools, pus and blood stools, mucus and blood stools. Blood bright red or dark red, in the form of drops attached to the surface of the stool; late often appear pus and blood stool and accompanied by anorectal cramps, wasting, stool habit changes and other symptoms. 1, painful blood in the stool 1, enteritis: often intermittent blood in the stool, the amount is small, and the stool contains pus and blood or mucus, accompanied by diarrhea, abdominal pain and urgency and other symptoms. 2, anal fistula: blood in the stool in small amounts, often mixed with stool, pus and blood or pus and mucus-like stool, bright red, with a feeling of urgency and pressure pain in the left lower abdomen, accompanied by abdominal pain, diarrhea and nausea, vomiting. 3, anal fissure: blood in the stool is irregular, sporadic, bright red, dripping out or blood after wiping with hand paper, severe pain in the anus during or after the stool.