Aiming at the leakage and diffusion problems of the 35 MPa ultrahigh pressure gas pipeline in densely populated area, the FLUENT software in the threedimensional numerical simulation was used under different climate conditions in the deep buried gas pipeline leak case. And the axial and surface safety area of the hydrogen sulfide and methane was provided when the ultrahigh pressure gas pipeline had leaked under the conditions of different wind speeds. Because of the buoyancy, the natural gas developed in the upward form during the process of diffusion. The wind speed and pressure had different effects on the diffusion process under the different environments. The result was that as the wind speed and pressure was higher, the natural gas was spread to the farther distance. This increased the lowest explosive limit and alerted the concentration range of the natural gas. The research result could provide the effective basis to the stuffs and security management in leakage spot.