Sudden vomiting of blood is not necessarily cancer, but can also be seen in conditions such as bleeding from the mouth. If a patient vomits a small amount of blood, the first thing to do is to observe whether the mouth is bleeding, such as the teeth, nose and throat, and to measure the blood pressure at the same time. If the blood pressure is too high, it can be treated with antihypertensive medication and ice saline gargle or cotton ball compression to stop the bleeding. Spitting up blood is also partially caused by hemoptysis due to bronchial dilation, pulmonary tuberculosis, or tumors. If the patient vomits coffee residue-like material with symptoms such as upper abdominal discomfort and tarry black stool, upper gastrointestinal bleeding is considered, and the patient is advised to fast from water and be treated with proton pump inhibitors and hemostatic drugs. Some gastrointestinal tumors may also cause sudden vomiting of blood, which is mostly caused by middle and late stage of cancer and tumor invasion of blood vessels. Sudden vomiting of blood is not necessarily cancer. The doctor should clarify the cause and take targeted treatment according to the results of blood routine, blood clotting mechanism, liver and kidney function, virus screening, gastroscopy and other examinations.