As cities grow,automobile exhaust pollution is worsening,which has become a major problem of air pollution,even it is a serious threat to the physical and mental health of residents.Thus,to study its diffusion law and influential factors occupies a count for much position.The paper analyzes the factors that affect the dispersion of urban vehicle emissions in street canyon to evaluate the research method of pollutant dispersion.In addition,the influences of different wind speeds and wind directions,the roof shape of buildings on both street sides,and the relative height of the two sides of buildings on the street canyon,on airflow field and pollutant dispersion are simulated.It is shown that the wind speed,the wind direction and the buildings on both sides have a great impact on the airflow and contaminant dispersion in the street canyon.The results provide scientific basis for controlling,monitoring and evaluating the urban motor vehicle emissions,besides the reasonable layout and the programme of urban streets.