The differences between pneumonia, lung cancer and tuberculosis are mainly in the following aspects: First, in terms of etiology, pneumonia is mostly caused by viruses or bacteria, fungi or atypical pathogens; whereas tuberculosis is caused by invasion of Mycobacterium tuberculosis; lung cancer is caused by the spread of cancer cells into the lung. The manifestations of pneumonia, lung cancer and tuberculosis are different in chest CT. Pneumonia is manifested as exudative lesions; lung cancer is manifested as occupancy and has lobes and burrs, which may cause pleural effusion and lymph node enlargement; tuberculosis is generally manifested as corn-like disseminated foci, and there are cavities in tuberculosis. Most of the symptoms of pneumonia are coughing, coughing sputum, chest pain and persistent high fever, while lung cancer and tuberculosis are thin and have low fever, hemoptysis and chest pain, and if the cancer cells invade the superior vena cava, it may lead to hoarseness due to compression of the recurrent laryngeal nerve. If the cancer invades the superior vena cava, it may lead to compression of the laryngeal nerve and hoarseness. Fourth, the prognosis is also different. Tuberculosis and pneumonia can be cured; while advanced lung cancer has a shorter survival period.