Lung cancer has the highest incidence and mortality rate worldwide and is the number one cancer in China, but early treatment can cure 80% of patients. There is still no effective screening and early diagnosis technique. Chest X-ray examination mainly helps to detect early peripheral type lung cancer, but its sensitivity is low, especially for small lung cancer diagnosis. Because of its high X-ray radiation dose, chest CT violates the principle of optimization of X-ray examination. In developed countries, routine spiral CT of the chest is also considered to be the most important cause of radiation of medical origin. Also, due to the higher cost of CT examinations, many patients are therefore apprehensive about chest CT examinations. Therefore, the current expert recommendation is that CT examinations may be required for people with high risk of lung cancer. People with high risk of lung cancer, i.e. those who are at higher risk and more likely to develop lung cancer. Specifically, they are: (1) Long-term smokers over 40 years old. (2) Long-term passive smokers. (3) Environmental pollution, air pollution (exhaust gas in diesel fuel) and indoor small environment pollution (such as frequent exposure to coal smoke or vegetable oil fumes during cooking and radioactive materials in decoration materials) for a longer period of time are also one of the risk factors for lung cancer. viV disease library, disease database, health information platform, your friend of health! The combustion products of coal, coal tar or other oils are carcinogenic. The incidence of lung cancer among gas, asphalt and coke workers is higher than that of the general population. (4) Occupational exposure to carcinogens. If the amount of exposure is high and the exposure time is long, the risk of lung cancer is high. The carcinogens of occupational lung cancer include asbestos, radon, nickel, chromium, arsenicals, dichloromethyl ether, chromium compounds, nickel compounds, soot, tar, polycyclic aromatic hydrocarbons in petroleum, radioactive substances polluted in mine air …… Long-term exposure to these carcinogens can cause cancer. (5) Patients with chronic lung diseases. Such as chronic bronchitis, tuberculosis, etc. The risk of lung cancer in these patients is higher than that of the general population . (6) If one of the family members has the disease, the risk of the rest of the family members will also be increased. (7) Patients with chronic cough, blood in sputum or positive sputum occult blood, especially those with irritating dry cough, chest pain, low fever and recurrent lung infections that do not resolve after aggressive anti-inflammatory treatment. Many early stage lung cancers may have these symptoms. It is important to be alert to these symptoms. (8) In addition, people with extra-pulmonary symptoms and signs, such as pestle and toe, sudden skin disease, dark complexion, high blood calcium, and unexplained joint pain, should also be further examined to prevent early lung cancer from being missed. When the possibility of malignancy of lung nodules is assessed to be small, follow-up of lung nodules should be done using CT. Pulmonary nodules of 〈5 mm should be reviewed by CT every 6 months, and those of 5-10 mm should be reviewed by CT every 3 months. Pulmonary nodules of 10 mm should be reviewed by CT every 1 to 2 months. Accelerated growth and solidity of nodules often suggest malignancy. If the patient’s condition allows, lung puncture or surgical resection is feasible to avoid delaying the diagnosis and treatment of early lung cancer.