Ground-glass patchy shadow of lung is not necessarily carcinoma in situ. Ground-glass-like density shadow can be seen in various kinds of pneumonia, tuberculosis, pulmonary edema and pulmonary infarction. Carcinoma in situ often involves the whole layer of epithelium, but does not break through the basement membrane and infiltrate downward, so it is non-infiltrative early lung cancer. Low-dose CT can effectively detect early lung cancer, which can be manifested as solid nodules, ground-glass-like density nodules and mixed density nodules according to its different densities. Ground-glass-like density of lungs is the lesion with light density, and blood vessels can be seen walking in the lesion, which can be seen in all kinds of pneumonia, tuberculosis, pulmonary edema, pulmonary hemorrhage and pulmonary infarction caused by pulmonary embolism. For example, in bronchopneumonia, X-ray shows that the lesions are distributed along the bronchial tubes, presenting speckled or patchy increased density; CT shows that the lesions are diffuse and scattered patchy shadows, with fuzzy edges. To summarize, lung ground glass patchy shadow is not necessarily carcinoma in situ, and it is recommended to go to the hospital and ask the doctor for diagnosis in time.