The duration of follow-up observation of lung nodules varies according to the density and size of the nodules, etc. Generally, it is required to repeat the examination in about 3 to 6 months, or once a year. 1. If the solid nodule is <6mm, review the CT in 12 months. 2. If the solid nodule is 6mm~8mm, review CT after 6~12 months. 3. If the solid nodule is >8mm, repeat CT in 3 months. 4. If multiple partially solid nodules <6mm, repeat CT in 3~6 months, and if the nodules are unchanged, follow up again in 2~4 years. 5. If partially solid nodules ≥6 mm, repeat CT in 3-6 months, and if the nodules persist, repeat CT every year for 5 years. 6. If multiple pure ground-glass nodules <6 mm, repeat CT in 3-6 months, and if the nodules remain unchanged, follow up in 2-4 years. 7. If pure ground glass nodule ≥6mm, repeat CT in 3~6 months, and if the nodule persists, repeat CT every 2 years in 5 years.