Shadow in the lung in CT examination refers to the high-density shadow in the lung parenchyma. At this time, the shadow in the lung can be manifested as mass shadow, nodular shadow, patchy shadow, solid shadow and so on. There are many causes of lung shadows, at this time lung shadows are not equal to lung tumors, as follows: 1, lung infection: patients can have lung shadows during lung CT examination, which can be manifested as patchy shadow, interstitial change, mass shadow, cavity shadow, etc. At this time, the degree of lung infection and the causative agent of infection should be specifically analyzed. 2, tumors: lung shadows can also be seen in benign lung tumors and malignant tumors. The lung shadow of lung tumor can present pulmonary ground glass nodule, pulmonary substantial nodule or mass shadow. Therefore, when the lung shadow is found in the CT of the lung, the relevant examination should be improved according to the situation, and some patients also need pathological biopsy to clarify the etiology and pathological nature.