Coughing up dark red bloody sputum can be caused by a number of factors, the most common being respiratory diseases. The most common causes are respiratory diseases, such as acute asthmatic bronchitis combined with severe infections, and acute pneumonia with severe lung infections, which can lead to rupture of the capillaries in the respiratory tract and hemorrhage. Secondly, it is also seen in various causes of bronchiectasis, obstruction of the lumen of the tube, chronic inflammation leading to rupture of the mucous membrane of the respiratory tract. It is also seen in rare bronchopulmonary carcinoma and alveolar carcinoma. In addition, it is also clinically seen in cardiovascular system diseases, such as left heart failure due to various reasons, which leads to obvious pulmonary edema and the rupture of capillaries, resulting in coughing up bloody sputum.