Under normal circumstances lung cavities larger than 4 centimeters or more are likely to be lung cancer. Lung cavity is formed after necrosis of diseased tissues in the lungs, which is discharged by draining bronchial tubes and inhaling gases, and it is an imaging manifestation. The result of this examination alone cannot directly diagnose lung cancer, and it is necessary to carry out related examinations to diagnose it, such as pathological examination, etc., to observe the structural changes of the tissue cells under the microscope to determine whether it is lung cancer or not. Lung cavity may be caused by tuberculosis, lung abscess, pneumoconiosis, etc. Its symptoms are thick-walled cavity, tension cavity, thin-walled cavity, chronic fibrous cavity, etc. Generally, the wall of the cavity is smooth, and fluid level is rare. On the other hand, the wall of cavity caused by lung cancer is usually irregular or uneven, and the size of the lesion is usually more than 4cm. Therefore, it is suggested that patients with lung cavities should actively go to the hospital for examination and cooperate with the doctor’s diagnosis and treatment, so as to avoid delaying the condition.