The causes of lung cancer are complex and the current research suggests that the following may be the causes of lung cancer Lung cancer is complex. Its occurrence is closely related to smoking and environmental factors. (1) Smoking: The constituents of tobacco and the smoke when burning contain 3-4 benzpyrene, arsenic, nitrosamines and other carcinogenic and pro-carcinogenic substances. According to statistics, 70-80% of lung cancer is caused by long-term smoking; smoking population lung cancer mortality rate is 10-20 times higher than that of non-smokers; the longer the smoking time, the more cigarettes smoked and the younger the age of starting smoking, the greater the chance of lung cancer; passive smoking in women, the incidence of lung cancer is more than 2 times higher than that of non-smokers in their spouses. (2) Occupational factors: Occupations related to asbestos, arsenic, chromium, nickel, coal tar and radioactive elements have a high incidence of lung cancer due to long-term exposure to carcinogenic substances. For example, the high concentration of arsenic and radioactive radon in the operating environment of tin mines in Jielao, Yunnan Province, is an important factor for the high incidence of lung cancer. (3) Air pollution: Air pollution caused by industrial exhaust, coal and gasoline combustion is known to be one of the factors for high incidence of lung cancer in urban than rural areas.