Lin Yutang said “a cigarette after a meal, happy life like a god”. For centuries, smoking is treated as a kind of enjoyment in life, people in the wine after dinner, often burn a cigarette, leisurely. But do not know, inhalation of tobacco smoke is leaching people’s lives, each cigarette, will reduce a person’s life six minutes. Smoking is the number one cancer-causing factor, especially lung cancer. Lung cancer is a disease that seriously endangers human health. According to the information published by the World Health Organization (WHO) in 2003, lung cancer ranks first in the world in terms of both incidence (1.2 million/year) and mortality (1.1 million/year). According to the Chinese Ministry of Health, in 2008, the mortality rate of lung cancer in the urban population was as high as 30.83/100,000, an increase of 465% compared to 30 years ago, and has replaced liver cancer as the leading cause of death from malignant tumors in China. More than 90% of these patients have a history of smoking . British oncologist R. Peto predicted that if China does not control smoking and air pollution in time, the annual number of lung cancer cases in China will exceed 1 million by 2025, making China the world’s largest lung cancer country. Numerous studies have shown that smoking is the primary cause of the progressive increase in lung cancer. The polycyclic aromatic hydroxyl compounds, nicotine, nitrosamines and a small amount of radioactive elements in cigarette smoke have carcinogenic effects, especially squamous epithelial cell carcinoma and small cell undifferentiated carcinoma. The incidence of lung cancer is twenty times higher than that of nonsmokers if they smoke twenty cigarettes a day for twenty years, i.e., the Law of Twenty. Second-hand or third-hand smoke is also a cause of lung cancer. The risk of lung cancer among non-smoking wives whose husbands smoke is twice as high as that of wives in non-smoking households, and the risk increases with the amount of smoking by the husband. On the contrary, the risk of lung cancer decreases year by year after quitting smoking, and can be halved after 1-5 years of quitting. The effectiveness of lung cancer treatment depends on early diagnosis. Long-term heavy smokers over the age of 40 should have annual medical checkups, and lung cancer mortality can be reduced by 20% by using low-dose spiral CT screening. Not smoking or quitting smoking early is the most effective way to prevent lung cancer.