Whether or not a ground glass nodule in the lower lobe of the left lung is serious depends mainly on the size and shape of the nodule, as follows: 1, not serious: if it is a relatively small ground glass nodule, less than 8 mm, and the nodule is smooth, no lobar, no vascular signs, vacuolar signs and other signs of malignancy, it is generally not serious, the most common cause or lung infection, of course, can also be seen in tuberculosis or old 2.Serious: If the nodule is larger than 8mm and there are signs of malignancy, such as lobar, burr, vascular and vacuolar signs, it may be a malignant tumor of the lung. In this case, further examination must be performed and surgical resection is necessary to further clarify the diagnosis. If a ground glass nodule in the lower lobe of the left lung is present, lung infection is considered and can be reviewed after two weeks of anti-infection treatment. If there is no change, the lungs should be reviewed periodically, for example, at three months, or at six months if there is still no change, and if there is still no change, the lungs should be reviewed periodically. If, during the follow-up, the nodule becomes larger, the density becomes uneven, or signs of malignancy such as the burr sign, lobar sign, vascular sign, or vacuolation sign mentioned earlier appear, further tests should be performed to make a definite diagnosis to exclude malignant lung tumors.