With the development of China's natural gas industry, the scale of natural gas pipeline transportation is also expanding, at the same time, it also brings the hidden danger of safety. The leakage accidents of urban natural gas pipeline occur frequently, which seriously affect the lives and property safety of urban residents. This paper mainly introduces the basic theory of numerical simulation and numerical simulation of the leakage of urban natural gas pipeline. Considering the influence of wind field on leakage, the variation of the wind field near the ground is analyzed, and the leakage model of the buried natural gas pipeline is established. The leakage diffusion is set in the atmospheric environment. The CFD software is selected to divide the grid and local encryption, and the steady state simulation of the wind field is carried out. After the wind field reaches the steady state, the boundary conditions of the post-processing are changed, and the leakage is simulated instantaneously. The variation law of the natural gas leakage diffusion with time is obtained, and the influence of wind speed on the leakage diffusion is analyzed quantitatively. The results show that the building has a disturbance to the wind field. During the leakage process, the gas gathers near the ground and close to the building. With the increase of wind speed, the steady-state diffusion height decreases, but the wind field has less influence on the horizontal diffusion. The greater the wind speed, the more obvious the dilution effect of the leakage gas, the smaller the dangerous area.