The research explored a mediator role of GDP on the relationship between life expectancy and environment based on data of twenty-three OECD countries for the period between 2004 and 2014. To provide empirical grounds for systematic research, the research employed two curve theories: Preston curve and environmental Kuznets curve. Then the research mapped out mediation model with four specific variables characterizing environment as predictor variables, life expectancy as an outcome variable, and GDP as a mediator variable. According to the findings, although the magnitudes of the effects which GDP mediates on relationships between each of four variables and life expectancy are different, it is clear that GDP mediates the relationships between life expectancy and each of the four specific variables. Given that the research exhibits a new approach to the study of the relationship between life expectancy and environment by setting up GDP as mediator, it is worthy of attention.