Black stools, which may be caused by dietary factors, drug factors, gastrointestinal bleeding, etc., are mainly identified by tracing the medical history, fecal character, and laboratory tests. 1. History: If the patient has a history of gastric ulcer and has been taking non-steroidal drugs such as aspirin and ibuprofen for a long time, we should consider the possibility of gastrointestinal bleeding; if the patient has been taking bismuth and iron drugs such as colloidal bismuth pectin capsules and ferrous sulfate tablets, we should consider that the black stool is caused by the drugs. 2. Stool properties: if the stool is tar-like black thin stool, we should consider the possibility of gastrointestinal bleeding, especially the color of the stool is bright, we should be more vigilant; if the stool is black in color, we can consider the constipation. 3. Laboratory tests: if the patient’s black stool is caused by gastrointestinal bleeding, the result of routine fecal examination is positive for occult blood, in addition, if the bleeding is very large, there will be the performance of blood routine, hemoglobin, red blood cell reduction, through the examination of renal function, you can see that the urea nitrogen is slightly higher than the normal value can indirectly suggest that the gastrointestinal tract has bleeding. The identification of black stools needs to be combined with the specific condition to choose the appropriate means of examination. It is recommended to consult a doctor promptly after the occurrence of black stools to avoid delaying the disease.