Dark stool can be considered from the following aspects: first, food intake, some food will be black stool after eating, such as blood products, black beans, black sesame, fungus, etc.. Second, drugs, a variety of drugs can cause the stool color black, such as a variety of iron, bismuth, etc.; third, pathological, the most common is the upper gastrointestinal bleeding. There are various causes of upper gastrointestinal bleeding, which can be acute mucosal damage to the stomach, including erosion, ulcers, or even tumors. Considering pathology or physiology, stool routine can be done to identify. If the stool routine is positive for occult blood, the possibility of gastrointestinal bleeding is considered and further clinical examination is needed.