The dispersion and distribution characteristics of the exhaust pollutants emitted by motor vehicles in the urban street canyons are mainly determined by the air flow structures, and there exists an important influence for the street layouts and configurations on the air flow structures. Based on solving the Navier-Stocks equation, the transport equation of the pollutant component and the standard k-ε turbulence model for 2D incompressible flow, the numerical solutions were obtained. Nine kinds of cross-section shapes of urban street canyons (two types) were constructed to study the effect on the pollutant dispersion within urban street canyons under 3 m/s for the inlet profile. The results show that the main vortex structure and pollutant distributions in the street canyon won't change due to the sinking of the vehicle lane. However, the pollution level in the motorway will increase as the sinking depth increases. In addition, the concentration distribution of pollutants in the corridor was greatly influenced by the height of the corridor. The average pollutant concentration on the respiratory plane near the leeward side increased by about 5% compared to the reference case (case 1). The corridor depth has little effect on pollutant dispersion in street canyon.