Left lung occupancy refers to a mass-like shadow in the left lung, which can be inflammation, benign tumor or malignant tumor, but the clinical term lung occupancy usually refers to the possibility of malignant tumor. However, whether the lung occupancy is inflammation or tumor requires further examination. If the left lung occupancy is found in chest CT, enhanced CT of the chest is needed to clarify the relationship between the lung occupancy and the surrounding blood vessels and the reinforcement of the lung occupancy. If the chest enhancement CT further suggests that the lung occupancy may be a malignant tumor, bronchoscopy or lung puncture is needed to clarify the pathological nature of the lung occupancy, and if it is a malignant tumor, treat it as early as possible.