This article focuses on the distribution characteristics of rain film on the surface of roof insulators in high humidity environments. Based on the aerodynamic calculation model of insulator flow field， combined with the discrete phase model and Enlerian wall film model methods， the process of high-speed airflow rain film generation and development on the surface of insulators is simulated. The system studies the influence of different wind speeds， rainfall intensities， and structural parameters such as the uptilt angle， dip angle， and spacing between insulator sheds on the distribution of rain film. And a high-speed droplet flow roof insulator power frequency withstand voltage test platform is built to analyze the impact of uneven distribution of rain film on the electrical performance of insulators. The research results show that under the condition of maximum wind speed and maximum rainfall intensity， the time for the average rain film thickness on the windward side of the insulator reaching the stability is the shortest. At the same time， the windward side of the insulator is directly affected by rain， and the average rain film thickness is greater than that of the crosswind side and the leeward side. Raindrops mainly collide with inertia on the windward and crosswind sides of insulators， while vortex collisions are predominant on the leeward side. At a high voltage of 27.5 kV and a wind speed of 40 m/s， there is droplet flow and discharge arc between the sheds on the leeward side of the insulator， and obvious droplet scattering can be observed near the edges of the sheds. As the uptilt angle of the shed increases， the thickness of the rain film gradually decreases. The influence of the dip angle of the shed on the thickness of the rain film is not significant. Considering the requirement for mechanical strength， it is recommended to use 0° dip angle. In addition， choosing a smaller shed spacing is beneficial for reducing the thickness of the rain film on the insulator surface.