Cavities in the lungs do not necessarily mean advanced tuberculosis. Tuberculosis, lung abscess, lung cancer, etc. may all lead to symptoms of lung cavitation. 1. Tuberculosis: it is the most common cause of pulmonary cavitation, mostly seen in the progressive stage of secondary tuberculosis. When Mycobacterium tuberculosis invades the lungs and produces caseous necrosis, these substances are expelled from the bronchial tubes through coughing, leaving round cavities in the lungs, thus forming pulmonary cavities. 2. Lung abscess: pus cavity will be formed after the infection of lung abscess, after the pus is drained out from bronchial tubes, lung cavity will be closed gradually with the self-repair of human body. 3. Lung cancer: Lung cancer patients’ lung cavities are generally due to the rapid growth of lung tumor, the blood supply is not enough, tumor necrosis occurs, and the necrotic tissues are discharged from the body through trachea and bronchial tubes, and then lung cavities will be formed. The etiology and morphology of cavities in different diseases have their own characteristics, and preliminary diagnosis can generally be made through lung CT examination.