Blood in the stool comes in bright red, dark red and black colors. It is mainly related to the site of bleeding, the amount of bleeding and the residence time of blood in the intestinal lumen. If the bleeding site is in the lower gastrointestinal tract and the amount of bleeding is large, and the residence time in the intestinal tract is short, the color of the bleeding is bright red; if the residence time is long, it will change to dark red. If the bleeding site is in the upper gastrointestinal tract and stays in the intestinal tract for a longer period of time, it will turn into black stool, which is due to the destruction of red blood cells and the release of hemoglobin that combines with sulfide to form ferrous sulfide in the intestinal lumen. If a patient has blood in the stool, he or she needs to go to the hospital as soon as possible, and the doctor will formulate an individualized diagnosis and treatment plan according to the specific condition.