Abstract: The cost-benefit analysis method was applied to evaluate the direct and indirect impacts of the implementation of national Ⅲ diesel vehicles' policies. Fully consider the influence of COVID-19 epidemic, two scenarios including business as usual(BAU)scenario and low-speed stability(LED) scenario were set based on different economic development level. The results showed that the eliminate part generated a net benefit of 66,400 yuan per vehicle and the restrict part generated a net benefit of 1,100 yuan per vehicle under the BAU scenario. While under the LED scenario, the net benefit was 59,900 yuan and 500 yuan per vehicle respectively.Viewed from the long-term and the entire social, economic and environmental system, the policies had good implementation performance. The policies promoted emission reduction and stimulating industrial transformation.