Solid micronodules in the upper lobe of the left lung have many have causes, such as lung inflammation, tuberculosis, pulmonary nodular disease or lung tumors. 1. Lung inflammation is often caused by bacteria such as Streptococcus pneumoniae, viruses such as influenza virus, mycoplasma and other infections, manifested as fever, cough, sputum, etc. Because of the infiltration or healing of inflammation, solid micronodules in the upper lobe of the left lung may appear or remain. 2. Tuberculosis caused by Mycobacterium tuberculosis infection, active tuberculosis or old tuberculosis foci can be manifested as micronodules in the upper lobe of the left lung. 3. Lung nodular disease or peripheral lung cancer caused by immune abnormality can also manifest as solid micronodules in the upper lobe of the left lung. After the discovery of lung nodules, further examination, such as chest CT, tumor markers, pathological biopsy, etc., should be taken to clarify the nature of nodules as soon as possible, and appropriate treatment should be carried out.