Lung nodular shadow is a dense shadow less than 3cm in the lungs found in CT examination. They are usually caused by pneumonia, lung cancer, tuberculosis and so on. 1. Pneumonia: localized exudation is caused by virus, bacteria, mycoplasma, chlamydia and fungal infections in both lungs, and nodular shadows can be found in CT examination. 2. Lung cancer: it is a malignant tumor originated from lung. It can be divided into adenocarcinoma, squamous carcinoma and non-small cell carcinoma, which can have symptoms such as coughing and sputum, hemoptysis, chest discomfort, etc. The imaging examination can have nodular shadow with irregular edge. 3. Tuberculosis: it is an infectious disease of lungs caused by Mycobacterium tuberculosis, the lesions are mainly in the lung airways and lung tissues, and there can be nodular shadows with fuzzy edges in imaging examination. There are many other causes of nodular shadow of the lungs, and it is recommended that patients should have regular follow-ups and determine the treatment plan under the guidance of the doctor.