Coughing up black blood may be due to the following reasons: First, coughing up blood caused by bronchial dilatation, because the amount of coughing up blood is relatively large, the blood may be dark red or black blood when it is coughed up if it has been in the body for a longer period of time, which may occur in patients with pulmonary tuberculosis. Second, coughing up black blood if it is blood, it may be caused by pharyngolaryngitis, pharyngolaryngitis patients who smoke or work or live in an environment where dust, smoke, haze is more serious, deposited in the respiratory tract may also cough up black blood clots or blood, but generally coughing up blood is small, it is possible to cough 1-2 times.