Abstract: In order to effectively support the city motorization process with control of pollution and congestion, the traffic index was established based on vehicle specific power (VSP) method for analysis of the vehicle emissions. Through the analysis of the traffic index micro vehicle travel speed distribution, massive data by the second operation and vehicle emission characteristic data were used to establish relationship of motor vehicle between the speed and emission factors on the real road. And taking Beijing city as an example, the research shows that the traffic index and passenger car NOx emission intensity has significant positive correlation between the types of road, between working days and weekends, between AM and PM, et al. The influence degree from big to small are the road types, difference between working days and weekends,difference between AM and PM.