Abstract: An integrated approach incorporating computational fluid dynamics(CFD) and GIS technologies is explored to model and simulate the movement characteristics of released gases and the concentration distribution around buildings at the street level.Some key technologies including street canyon modeling,continuous field representation,numerical simulation and visualization of gas dispersion are presented.As a case study,a hypothetical continuous release from a point source is modeled and simulated.The results show that,the proposed approach is able to predict the 3D and dynamic dispersion process in urban streets.The time-varying concentration distributions near the ground highlight the influences of building arrangement on the dispersion.The sampling concentrations around buildings are strongly affected by the positions of sampling points relative to source,including difference in height,distance from the source,and angle from wind direction.The results also confirm that,in the streets the hazardous gas may stay longer,which constitutes a threat to public health and safety.