Abstract: Leakage simulation of gas is carried out for a damaged urban gas pipeline with established 2D and 3D CFD analysis models. The result shows that the gas dispersion is greatly impacted by windspeed and buildings. The higher the windspeed is, the stronger the gas transfer effect of wind along the downwind direction is, which speeds up the gas diffusion. And the highly dense gas gathered around building will surge over the building and form a dangerous zone around the building. The canyon effect of the street also has certain impact on the gas dispersion for the pipeline leakage under the ground. The CFD (Computational Fluid Dynamics) analysis assists the urban gas pipeline safety management, risk assessment, accident investigation and emergency measures.