A normal colonoscopy with blood in the stool may be the result of anal canal disorders such as hemorrhoids and anal fissures, or bleeding in the small intestine, stomach, or duodenum area. Enteroscopy is a method of examination in which the enteroscope is inserted from the anus and reaches the ileocecal part along the intestinal canal, mainly checking for lesions in the rectum and colon, and a normal enteroscopy usually indicates that there are no obvious lesions in the colon and rectum. However, colonoscopy does not visualize lesions in the small intestine and above (stomach, duodenum, etc.) and the anal canal. When bleeding occurs in these places, a normal colonoscopy with blood in the stool may occur. 1. Anal canal diseases: such as anal fissure, hemorrhoids, etc., the mucous membrane and blood vessels at the patient’s anal canal are relatively fragile. But then the blood is usually on the surface of the stool, the patient will also be accompanied by pain in the anus. 2. Bleeding in the small intestine: Inflammatory bowel disease, polyps in the small intestine, diverticula, vascular malformations or malignant tumors of the small intestine can cause patients to have blood in the stool, which is usually mixed in the stool, and the patients will also have abdominal pain and bloating, loss of appetite and other symptoms. 3. Gastric or duodenal bleeding: such as esophagogastric fundus varices rupture or peptic ulcer caused by gastric, duodenal bleeding or perforation, etc., will make the patient have blood in the stool, and accompanied by acid belching, abdominal pain, dizziness, fatigue and other symptoms. When the patient has blood in the stool enteroscopy is normal, it is recommended to consult a doctor in a timely manner, under the guidance of the doctor to carry out targeted treatment, so as not to delay the condition.