Primary bronchial cancer, or lung cancer for short, is a malignant tumor originating from the mucosa or glands of the bronchi, which seriously endangers the health of human beings. The etiology and pathogenesis of lung cancer are not yet clear, but it is usually believed to be related to the following factors: 1. Smoking. Studies have shown that smoking is the primary cause of progressive increase in lung cancer mortality. The benzo(a)pyrene, nicotine, nitrosamines and small amounts of radioactive elements such as polonium mixed in cigarette smoke have carcinogenic effects. Passive smoking or environmental smoking is also a cause of lung cancer. The risk of lung cancer will be reduced year by year after quitting smoking. 2.Air pollution. Including the small indoor environment and the large outdoor environment. Indoor passive smoking, burning fuel and oil fumes released from cooking may produce carcinogens. Atmospheric pollution is one of the important causes of lung cancer because of the presence of carcinogens such as arsenic oxide, radioactive substances, nickel and chromium compounds in the polluted atmosphere. 3. Occupational carcinogenic factors. Occupational factors that have been identified to cause human lung cancer include asbestos, arsenic, chromium, nickel, radon, mustard gas, trichloromethyl ether, heating products of tobacco and ionizing radiation and microwave radiation produced by the decay of radioactive substances such as uranium and radium, among which asbestos is a recognized carcinogen, and the incidence of lung cancer, pleural and peritoneal mesothelioma is significantly higher in the dischargers. 4.Diet and nutrition. Studies have shown that less consumption of vegetables and fruits with beta carotene increases the risk of lung cancer. 5.Other predisposing factors. Tuberculosis, viral infection, fungal toxins (aflatoxin), etc. may also play a role in the occurrence of lung cancer. 6.Heredity and genetic mutation. The above exogenous factors may induce malignant transformation of cells and irreversible genetic changes, thus leading to uncontrolled cell growth and carcinogenesis. Prevention: Avoiding exposure to factors related to the development of lung cancer, such as smoking and atmospheric pollution, strengthening labor protection in occupational exposure, and consuming more green, yellow and orange vegetables and fruits containing β-carotene and foods containing vitamin A can help reduce the risk of lung cancer development. There are no effective chemopreventive measures for lung cancer, and non-smoking and early smoking cessation may be the most effective way to prevent lung cancer.