Coughing up blood in the mouth is considered to be caused by bronchiectasis, tuberculosis, lung cancer and other diseases. 1. Bronchiectasis: Bronchiectasis can be triggered by respiratory infections and bronchial obstruction. Secondly, low immunity or chronic respiratory diseases may also trigger bronchiectasis, resulting in coughing up blood in the mouth, breathlessness, coughing, increased sputum and other symptoms. 2. Tuberculosis: If the patient’s lungs are infected with Mycobacterium tuberculosis, it is easy to induce tuberculosis, resulting in patients coughing up sputum, chest tightness, coughing up blood and other symptoms. Tuberculosis is an infectious disease, which can be spread through droplet channels. 3. Lung cancer: Lung cancer patients may also have symptoms such as coughing up blood, hoarseness, chest pain and coughing up sputum. Acute pharyngitis and acute bronchitis may also be the causes of coughing up blood in the mouth. Meanwhile, it should also be differentiated from vomiting blood caused by digestive system diseases, such as perforated gastric ulcer and cirrhosis of the liver, etc. It is suggested that patients should go to the hospital for relevant examinations to find out the causes of the disease and treat it actively.