Coughing up blood may be caused by tuberculosis, bronchiectasis, lung cancer and other diseases. 1. Tuberculosis: Tuberculosis patients’ foci erode blood vessels, causing damage to blood vessels, the size of the damaged blood vessels with different degrees of damage, hemoptysis is different. Inflammatory reaction of tuberculosis foci and the stimulation of toxins on the capillary wall make the capillary permeability increase, red blood cells extravasate to the alveoli, and the symptom of blood in sputum appears. 2. Bronchial dilatation: due to chronic suppurative inflammation and fibrosis of the bronchial tubes and the surrounding lung tissues, the muscles and elastic tissues of the bronchial walls are destroyed, resulting in deformation and persistent dilatation of the bronchial tubes. Symptoms of hemoptysis will appear. 3. Lung cancer: when there is tumor in the lungs, it will cause inflammation and edema of local tissues, which will increase the permeability of capillaries, and blood will flow into the respiratory tract. Blood will flow into the respiratory tract. Hemoptysis will also occur when the tumor presses the microvessels and causes the blood vessels to rupture. In addition to the above, hemoptysis can also be seen in leptospirosis, lobar pneumonia, pulmonary infarction, acute heart failure and other diseases. When hemoptysis occurs, it is recommended to consult a doctor for further investigations, to identify the cause with the help of the doctor, and to carry out targeted treatment or therapy.