Diarrhea and black stools are generally considered for two reasons. On the one hand, we should consider whether the black stool is caused by the recent consumption of animal blood, liver and black food. It is also possible that the black stool is caused by taking Chinese herbal medicine or bismuth such as potassium citrate. These factors cause black stools which are physiological in nature and usually do not require special treatment and will be relieved after complete excretion of food or discontinuation of medication. On the other hand, we should consider whether the black stool is caused by gastrointestinal bleeding, which needs to be clarified by routine stool examination. If it is clear that the bleeding is from the gastrointestinal tract, further examination of colonoscopy and gastroscopy should be done to clarify the exact location and cause of the bleeding, and then further treatment should be given to avoid anemia due to prolonged bleeding.