It is very valuable for decision-making on automotive pollution control to quantify the pollutant emissions from motor vehicles. Based on the determining of important parameters by testing Chinese vehicles, MOBILE5 model was used to calculate the composite emission factors of the vehicle fleet in Beijing. The overall emission amounts and the contribution rate of automobiles were achieved for the urban areas as well as the whole city. The sharing rate of different types of vehicles to the total vehicular emissions in urban areas was analyzed. Results showed that the contribution rate of mobile sources are 78%, 83% and 46% respectively for the total emissions of CO, HCs and NOx in urban areas.