Yellow stools with black streaks may be caused by physiological factors such as diet and medication, or it may be caused by gastrointestinal bleeding due to gastrointestinal diseases and blood system diseases. 1. Physiological factors: If the patient has recently eaten a lot of melanin-rich substances, such as black fungus, black sesame, black beans, seaweed, etc., it will make the color of the stool darken, and the situation of yellow stool mixed with black stripes will appear; taking certain medications, such as iron, bismuth, etc., will also make the stool darken, and the stool will be yellow mixed with black strips of change. 2. Diseases of digestive tract: such as peptic ulcer, esophagogastric fundus varices, gastric mucosal prolapse, gastrointestinal cancer and other diseases, when there is gastrointestinal bleeding, it may cause black stools, resulting in yellow stools mixed with black streaks. 3. Blood system diseases: such as hemophilia, leukemia, hemolytic anemia, aplastic anemia, allergic purpura and other diseases, may also cause bleeding, when the blood enters the digestive tract with the discharge of stool, it may also cause the stool to become black, stool yellow mixed with black stripes of phenomenon. If the patient has the above situation for a long time or repeatedly, it is recommended to consult a doctor in time to find out the cause of the disease under the guidance of a professional physician and carry out targeted treatment to avoid delaying the condition.