Radon is a radioactive gas existed in human environment. Main human effect of radon exposure is to increase lung cancer risk that is evidenced by epidemiological study among miners who received high level of radon exposure. Research on effect of radon concentration in living environment belongs to study of low dose effect of ionizing radiation. According to the hypothesis of ？？linear model without threshold？？, indoor lung cancer risk could be derived from miner study. But there are important differences between miners and residents, such as radon levels, confounding factors, constituent of study groups and so on. It is necessary to demonstrate directly the excess risks from residential radon and confirm miner extrapolations.

The large-scale epidemiological investigation was conducted in Pingliang and Qingyang Prefectures in Gansu Province with population of 4.2 million. The result is that lung cancer risk increased with increasing radon level. When a linear model was used, the excess odds rations at 100 Bq/m3 were 0.19 for all subjects and 0.31 for subjects for whom coverage of the exposure interval was 100%. Adjusting for exposure uncertainties increased estimates by 50-100%. Results support increased lung cancer risks with indoor radon exposures that may equal, or exceed extrapolations based on miner data. Based on the database established in the study, other factors influenced in lung cancer risk were also analyzed: OR for ever exposed to ETS in childhood, compared with ETS exposure in adulthood, is high. There is close relation between coal combustion and lung cancer risk. PAH and PM10 contents in coal using room is much higher than that in biomass using room. Women exposed to fumes from cooking oil (especially rap seed oil) appeared to be at increased risk of lung cancer. Additional evidence is provided from this study: pulmonary tuberculosis and chronic bronchitis/emphysema are causally related to lung cancer. OR of lung cancer were lower for later ages at menarche and later ages at menopause.