The severity of a ground glass nodule in the upper lobe of the left lung depends on the size of the nodule and the nature of the nodule. If the nodule is less than 5 mm or even 3 mm, it is called microscopic nodule, which is mostly benign and does not require special treatment, and the patient is advised to follow up with a high-resolution CT of the chest once a year. if the nodule is between 6 and 8 mm and grows progressively, it is more likely to be considered a malignant tumor, and the patient is advised to have an enhanced CT of the chest as soon as possible, or to have an early surgical intervention by a thoracic surgeon. If the left upper lobe ground glass nodule is larger than 8mm and accompanied with typical lung cancer changes such as short burr, lobar pattern, pleural pulling sign, pleural depression sign, etc., enhanced CT of the chest should be performed as soon as possible, and if necessary, a thoracic surgeon should be consulted to perform surgical resection and obtain pathological biopsy as soon as possible to clarify the diagnosis and whether radiotherapy, chemotherapy and gene therapy are needed after surgery. Therefore, the severity of the left upper lung ground glass nodule depends on the size, growth pattern and nature of the nodule, especially the result of pathological examination, if it is inflammatory, it is not serious, if it is malignant, it is a serious result.