This topic to take large multicenter study real world, the advanced liquid biopsy will ctDNA methylation detection technique is applied to pulmonary nodules differential diagnosis and early lung cancer screening, validation of early lung cancer screening and diagnosis of molecular classification system model, the feasibility of the development of early lung cancer screening and diagnosis of molecular classification system, improve its early screening early detection accuracy and efficiency, Improve the survival status of lung cancer high-risk population. At the same time, this project combined AI analysis technology of LDCT image results with ctDNA methylation detection, so as to overcome false negatives caused by the deficiency of ctDNA methylation detection technology in sensitivity, specificity, stability and flux, and correct false positive results that may be caused by AI analysis technology of LDCT image results. The combination of the two can avoid missed diagnosis and over - examination and over - treatment.