The left lung nodular shadow suggests inflammatory or occupying changes in the lung. The nodular shadow needs to be initially screened for inflammatory, tuberculosis or neoplastic changes based on the size and nature of the nodule. Generally, left pulmonary nodular shadow less than 5 mm is mostly benign and only requires dynamic follow-up of chest high-resolution CT once a year. If the nodule shows growing changes between 6-8 mm, the left lung nodule needs to be highly alerted to the tendency of early malignant changes, and thoracic surgery should be requested. If the left lung nodule is larger than 8mm, accompanied by short burr, lobar shape, pleural pulling sign, pleural depression sign, especially with blood in sputum and progressive wasting, it is more important to highly suspect whether the nodule has cancerous changes, give enhanced CT examination of the chest, and ask thoracic surgery to remove the nodule if necessary for treatment.