Sudden vomiting of blood is not necessarily cancer, but can also be seen in oral bleeding, etc. Specific analysis is needed for each problem. If a patient vomits a small amount of blood, first of all, we need to observe whether the mouth is bleeding, such as teeth, nose and pharynx, and at the same time, we should measure blood pressure. If the blood pressure is too high, medication can be given to lower the blood pressure and ice saline gargle or cotton ball compression can be given to stop the bleeding. If the patient vomits coffee-colored stomach contents or coffee-colored blood with upper abdominal discomfort and tarry black stool, upper gastrointestinal bleeding is considered, and the patient is advised to fast from water and given proton pump inhibitors and hemostatic drugs to treat the bleeding. In addition, some patients with gastrointestinal tumors may also suddenly vomit blood, which is mostly caused by tumor invasion of blood vessels in the middle and late stages of cancer. Therefore, vomiting blood may not necessarily be cancer. The doctor should clarify the cause and provide timely treatment according to the results of blood routine, blood clotting mechanism, liver and kidney function, virus screening, gastroscopy and other tests.