Abstract: In view of the problem of buried gas pipeline piercing leakage outside the buildings, a three-dimensional simulation model was established with Gambit2.4. The continuous leak diffusion circumstance of gas in soil and atmosphere were carried out through numerical modeling by CFD software Fluent 14.0 under different ambient temperature and humidity. The influence factor of gas diffusion and the distribution regularity of concentration were comparatively analyzed under the coupling effect of ambient temperature and relative humidity. The research result showed that the gas ejecting from the leakage mouth first spread rapidly in the soil layer, resulting in the concentration of the upper surface quickly reaching the lower explosive limit and upper explosive limit. As the gas permeating through the earth surface, it influenced both sides of the building. Different concentration diffusion regions also formed on the windward side and the leeward side direction. Affected by different humidity and temperature, for some buildings, the warning concentration on the height of surface changed obviously. The case study results could assess the scope of the gas leak accident and effectively evacuate the masses in time.