Vehicle emission is the main culprit for the air pollution in the city. Through the camera capture and image recognition method, the information about vehicle volume is obtained. Combined with the information about vehicle emission factors that is published by the Ministry of Environmental Protection, the emission intensity of the streets is calculated. Then based on the model of turbulence and the theory of porous media, the flow field and pollutant concentration distribution in street canyon are obtained by computer numerical simulation. The data obtained can provide a scientific basis for the urban street design and exhaust pollution control measures.