The construction of urban underground road can effectively alleviate the increasingly crowded urban traffic conditions.But due to urban traffic characteristics,the treatment of vehicle emissions cannot simply copy the existing highway design code.Grasping the emission characteristics of the major pollutants of motor vehicles in the urban underground road has a very important guiding significance to urban tunnel ventilation system design criteria and design method.Taking the first tier cities like Beijing and Shanghai and the second tier cities like Wuhan,Nanjing and Guangzhou as objects,through inspecting the motor vehicle population,vehicle type,traffic flow,speed and other parameters,the influences of different urban traffic characteristics on the vehicle emission factors were analysed.The results can provide the basis for the further determination of pollutant emission factors and lay down the foundation for the tunnel ventilation design.