Ground glass lung shadow is not necessarily cancer. Pulmonary ground glass shadow is a focal, well-defined, increased density shadow in the lung on CT chest scan, which is not enough to cover the bronchial vascular bundles that travel in it, and is divided into pure ground glass shadow and partially solid ground glass shadow according to whether it contains solid components. Patients with inflammation, bleeding, infection, allergy, tuberculosis, and tumor can have ground glass shadow. Partial solid ground glass shadow with solid component ≥6mm is early stage lung cancer. Ground glass shadows with specific signs suggest possible lung cancer, such as burr, lobar, pleural fold, and bronchial inflation signs. Even if it is lung cancer, most patients are early stage lung cancer, so ground glass shadow in the lung is not necessarily lung cancer.