Based on the real time data monitoring system of motor vehicle emission in Nanjing city.This paper briefly describes the effect of Nanjing automobile emission reduction .In the "Twelfth Five Year Plan" period, Nanjing City motor vehicle retains the 71.8% growth, implementing the pollutant emissions reductions by 18.8 and average emissions of CO, HC, single NOx fell by 33%, 31% and 36% compared with 3 years ago; emission standard and analysis of variance showed its effect on NOx, CO and HC emission value from big to small order are: The quality of oil > emission standard > Life. Thus it is very important to enhance the quality of oil.