Sudden coughing up bright red blood may be pneumonia, tuberculosis, bronchiectasis, lung cancer, pulmonary embolism and so on. 1. Pneumonia: the lungs are infected with bacteria, fungi, viruses, mycoplasma and other pathogens, the main symptoms are coughing, coughing up pus sputum, coughing up blood sputum, fever, etc., perfect sputum culture, blood test, chest X-ray and other tests can be a clear diagnosis. 2. Tuberculosis: the lungs are infected with Mycobacterium tuberculosis, the typical symptoms are coughing, coughing up bloody sputum, low-grade fever, night sweats, etc., and the diagnosis can be clearly made by perfecting sputum culture, antacid staining, tuberculin test and chest X-ray. 3. Bronchial dilatation: long-term and repeated chronic bronchial infection causes bronchial deformation, the main symptoms are coughing up a large amount of purulent sputum, coughing up bloody sputum, fever, etc. Improvement of blood routine, sputum culture, chest imaging can be clearly diagnosed. 4. Lung cancer: there are no obvious symptoms in the early stage, but in the late stage, coughing, coughing up bloody sputum, unexplained weight loss, hoarseness and other symptoms, perfect chest imaging, tumor markers can be used to assist in the diagnosis, and lung tissue biopsy can be used to make a clear diagnosis. 6. Pulmonary embolism: it is an emergency, with acute onset, sudden coughing up blood, chest tightness, shortness of breath, chest pain, perfect D-dimer, coagulation function, angiography, lung imaging can be clear. Sudden coughing up bright red blood has many other causes, it is recommended to consult the respiratory medicine department of the regular hospital in a timely manner to clarify the cause of the disease, so as not to delay the condition.