There are many reasons why vomit and stool are black, but they are usually related to gastrointestinal inflammation, gastrointestinal ulcers, and a few people may be caused by gastrointestinal tumors, so it is recommended to seek medical advice and treatment in a timely manner, combined with routine stool and gastroscopy. 1, gastrointestinal inflammation: gastrointestinal inflammation will lead to congestion of the gastrointestinal mucosa, and will be accompanied by increased secretion of gastric acid, too much gastric acid stimulation can lead to Gastrointestinal mucosa breakage, the mucosa breakage will appear bleeding in the gastrointestinal tract, the outflow of blood after the role of digestive juices and oxidation, it will make the vomit and stool appear black; 2, gastrointestinal ulcer: gastrointestinal ulcer is the gastrointestinal tract mucosa breakage or erosion, the mucosa breakage of blood will flow into the gastrointestinal tract, in the gastrointestinal tract after digestion, it will lead to vomit and stool appear black, the reason is The blood is oxidized by gastric acid and the oxidation of divalent iron ions into trivalent iron ions. 3. Gastrointestinal tumors: Gastrointestinal tumors become larger in the process of growth and may rupture and bleed, or squeeze the gastrointestinal tract causing the mucous membrane of the gastrointestinal tract to break and bleed, followed by black vomit and black stool. If vomit and stool appear black, accompanied by fever, abdominal pain, diarrhea, shortness of breath, weakness, emaciation, blood in stool and other symptoms, medical treatment should be sought in time.