Risks in gas transportation are usually comprised of losses of the valuable gas, fire, explosion, and destruction to the environment. The safety of this infrastructure especially flammable gas pipelines is of great importance due to potential associated risks when leakage happens. An accurate understanding of the dispersion characteristics of the leaked gas from the underground pipe is of great importance. A gas leaking model from the buried pipeline was established based on computational fluid dynamics (CFD) technique, to simulate the situation. At the incidence of leakage, gas will propagate out and cause changes in flow behavior, which will prompt the detectors. The leakage position influences significantly much on the strength of leak signals to be detected at the ground surface. Under the simulation process, the double leakage pipeline model was involved. The variation of flow parameters inside the pipeline, outside pipeline, and the effect of leakage position were depicted and analyzed.