The predisposing factors of lung cancer are 1, smoking and passive smoking 2, air pollution 3, occupational factors 4, previous lung lesions 5, genetic factors Therefore, the people who need to be screened for lung cancer are: 1, smoking more than 20 cigarettes per day, smoking age greater than 20 years long-term smoking, age up to 55 years old and their family members. 2.Housewives. 3.Living in air pollution environment for a long time, age over 45 years old. 4, high-risk occupations such as exposure to gas, asphalt, coking, dust, mining, chemical. 5.Previous lung-related diseases: tuberculosis, old and slow bronchial, bronchiectasis. 6.People with family history of tumor.