If a patient with gastric cancer vomits black watery stuff, it means there is upper gastrointestinal bleeding. For this black substance, it is coffee-like gastric contents to be exact. Gastric cancer often causes upper gastrointestinal bleeding because there will be erosion and ulcer at the same time, and when the erosion and ulcer foci invade the blood vessels, it will cause the symptoms of bleeding. Patients are advised to go to the hospital in time and cooperate with doctors for examination and treatment, applying symptomatic support treatment such as acid suppression, hemostasis, blood transfusion and fluid replacement. Also, in case of upper gastrointestinal bleeding, it is necessary to cooperate with fasting or cold liquid diet, that is, not to drink hot things, to avoid bleeding as well as further aggravation of the condition.