Abstract: During preparations for the Olympic Games, Beijing issued a series of environmental policy, increased environmental governance. By using synthetic control method which appeared in comparative case study recently, we estimated the impact of the Beijing 2008 Olympic Games on Beijing's air quality in this paper. The results showed that Beijing's air quality has been significantly improved after 2008; average annual air pollution days reduced 25 days, and the result is significantly on the level of 3.2%. But after 2010, the effects of environmental policy on Beijing air quality disappeared gradually. Furthermore, considering winter is the most polluted season of Beijing, this paper further examines the impact of the Olympic Games on the air quality in winter, we find that after the Olympics, the improvement of air quality in Beijing mainly occurred in other seasons, winter air quality did not significantly improved. Finally, for the perspective of China’s long-term economic growth pattern, local official evaluation mode and China’s local environmental politics, this paper analysis the reason why the environmental policies can’t improve air quality in the long time.