Many diseases can cause coughing up blood, mainly in the respiratory system and cardiovascular system diseases, as follows: 1. Respiratory system diseases: bronchial diseases such as bronchial dilatation, bronchial tuberculosis, bronchial lung cancer, etc. Lung diseases commonly include tuberculosis, pneumonia, lung abscess, and less commonly pulmonary embolism. 2. Cardiovascular system diseases: cardiovascular system diseases more commonly include mitral stenosis, cardiac insufficiency, and some acute infectious diseases, rheumatic diseases, etc. can also cause coughing up blood. Inadequate, and some acute infectious diseases, rheumatic diseases, etc. can also cause coughing up blood. Coughing up blood refers to bleeding from the larynx, the respiratory tract below the larynx, or any part of the lungs, and coughing up blood through the mouth is called coughing up blood. Because the blood is discharged from the mouth, it is necessary to carefully identify whether the bleeding is from the mouth, nasal cavity, or gastrointestinal tract.