Ice and snow accretion on transmission lines seriously threatens the secure and stable operation of the power system. Current research focuses on the discharge development and flashover characteristics of snow-covered insulators. Due to the complexity of the insulator, the growth of snow accumulation remains a lack of systematic analysis. In this paper, based on computational fluid dynamics (CFD), the local impact characteristics of snow particles on XP-70 insulator were simulated and analyzed under different environmental parameters, subsequently, a three-dimensional numerical calculation model was established. The results show that there are two opposite processes during flow around an insulator, namely, the pressure decrease accompanied by the increase of the velocity as well as the increase of the pressure with the decreasing velocity. Local collision coefficient on the windward side of the insulator gradually decreases along with the steel or the shed from the front stagnation point to both sides. The coefficient at the edge of the shed and the steel cap of the windward side of the insulator is much higher than that of other positions, and the maximum value can reach 0.74. Snow accumulation on the insulator increases with the increase of v，liquid water content (LWC) and median volume diameter (MVD). Its maximum is 2.19 kg. It is verified by the simulation and test that snow accretion is the heaviest at the location where the local collision coefficient is the largest, and the error between the two is less than 17%.