Patients with blood in the mouth are generally considered to have upper gastrointestinal bleeding, but it is important to first exclude blood coughing up from the respiratory tract from the mouth, as well as bleeding from the mouth, nose and pharynx from the mouth. Common causes of upper gastrointestinal bleeding include the following: First, peptic ulcers: including anastomotic ulcers. Second, benign tumors: including smooth muscle tumors, adenomas, lipomas, fibromas, neurofibromas, etc. Third, malignant tumors: including esophageal cancer, gastric cancer, smooth muscle sarcoma, lymphoma-like cancer, etc. Fourth, metastatic tumors: including melanoma, breast tumors, pancreatic tumors, lung and kidney tumors metastasis. Fifth, other etiologies: such as erosive gastritis, erosive esophagitis, erosive duodenitis, esophagus-pancreatic mucosal tear syndrome, ruptured esophagus-fundus varices, vascular malformations, etc. This is a common cause of upper gastrointestinal bleeding. When patients have blood in the mouth, they must pay attention to it and go to the hospital in time for relevant examinations to clarify the cause and give comprehensive treatment to prevent delaying the disease.