Abstract: Based on the CFD simulation, the impacts of ground open floor on flow field distribution and vehicle exhaust dispersion inside an isolated street canyon were studied. The numerical simulation results revealed that open floor was good at contamination diffusion in the street canyon. The diffusion effect of setting open floor in the direction of wind flow is better than that in the leeward direction. The most favorable situation is that open floor is set on both sides of the street. The research results could provide reference for urban planning.