Smoking can lead to lung cancer, but not always, that is, it is a matter of probability. The probability of getting lung cancer from smoking is higher than that of non-smokers, generally around 20-50 times, because smoking is the most common risk factor for lung cancer in medical science. Lung cancer is a malignant tumor of lung tissues, which is caused by many reasons and has a complex mechanism of occurrence, among which the most common cause is long-term smoking, in addition to environmental factors such as air pollution, as well as exposure to chemical materials such as asbestos and genetic factors. Therefore, in order to avoid lung cancer, the first step is to quit smoking, including avoiding the harm of second-hand smoke, in order to reduce the probability of getting lung cancer.