0.4 cm lung nodule can be left untreated for the time being, and attention should be paid to follow-up observation. If the nodule continues to increase in size, further examination, such as pathological biopsy, can be done, and surgical resection should be considered if the nodule is malignant. In general, 0.4 cm nodules do not require treatment, but should be reviewed regularly to see if there are any changes in the nodules, such as the size of the nodule has become larger, the number of nodules has increased, etc. If there is a significant increase in the size of the nodule, the nodule should be removed. If the nodule has an obvious tendency to increase in size, it is necessary to cooperate with the doctor to do chest enhancement CT, MRI, bronchoscopy as well as sputum culture examination, pathological biopsy, etc. If necessary, consider surgical treatment, such as removing part of the lung lobe. If a 0.4 cm pulmonary nodule is found, it is recommended to cooperate with a specialized doctor to strengthen the examination to clarify the size and nature of the nodule. If the nodule is determined to be malignant, or if the nodule continues to grow, surgical resection should be considered as soon as possible. After surgery, we should also have regular checkups and pay attention to dietary modifications, with light food as appropriate. At the same time, it is important to stay away from dusty environments and smoking environments to avoid lung irritation.