The prevalence of small pulmonary nodules is in the range of 20-30%, with a relatively high incidence of small pulmonary nodules. With the current application of low-dose spiral CT in lung disease screening, more and more lung nodules are detected. For lung cancer screening in China is also being carried out gradually, and the Fourth Hospital of Hebei Medical University has performed low-dose spiral CT for lung cancer screening on people in high lung cancer incidence areas after several years since January 2014-December 2017, and found 2786 cases, accounting for 31.2% of the entire follow-up population, with at least one nodule in the lung. Another set of data is the US lung cancer screening, based on a high-risk population for lung cancer. 53,439 high-risk patients were screened, half of whom received low-dose spiral CT, and 24.2% were detected as having a lung nodule, but only 3.6% of these patients with lung nodules were diagnosed with lung cancer. The development of small nodules is not strongly related to gender and can occur at any age, but is more common in persons aged 40-65 years. Nodules with a diameter of 3 cm are not clinically considered as a key observation target because they are too small and have a relatively low chance of malignancy, and in the process of gradual growth if long-term follow-up is performed, it will take longer time. However, when the diameter of nodules exceeds 6 mm, regular follow-up is needed to rule out the possibility of early lung cancer.