Using the method of qualitative and quantitative combination, the risk identification and pre-risk analysis of CNG filling stations were carried out by using the principle of system safety engineering. And the FLACS software based on computational fluid dynamics was used to simulate the accident situation of the filling station leakage. The influence of different wind speed on the leakage accident and the different ignition position on the explosion accident were studied, so as to provide the data support for the design of the safe distance and the safety barrier to reduce the accident risk. The results showed that the volume of the gas cloud increases rapidly within a few seconds of the beginning of the leakage, but the volume of the gas cloud exploded in a stable state over time; the larger the wind speed was, the farther the diffusion distance of the gas cloud, but the actual dangerous concentration volume gradually decreased; different ignition locations would cause different over-pressure, where the edge of the ignition caused by the explosion over-pressure was greatest and the center ignition produces an explosion over-pressure minimum