Abstract: The roof insulator is an important component of the high-speed EMU train. During the operation in high altitude areas, the negative pressure area is formed by the wind pressure distribution around the roof insulator under the action of high-speed air flow, resulting in its comprehensive air pressure far lower than the air pressure corresponding to the actual altitude, thus affecting the electrical performance of the roof insulator. Based on the computational fluid dynamics (CFD), this paper establishes a simulation model to analyze the wind pressure distribution characteristics and the influencing factors around the top insulator under the high-speed air flow. It proposes a method for correcting the electrical strength of the top insulator under the comprehensive action of the high-altitude high-speed air flow. The simulation results show that the low wind pressure of the roof insulator is distributed at the root of the umbrella skirt on the crosswind surface (i.e. at the root of the lower surface under a large umbrella and at the root of the upper surface under a small umbrella); The absolute values of the wind pressure on the windward side, the leeward side and the crosswind side all increase exponentially with the increase of the wind speed, and the lower the altitude, the faster the increase; When the angle of attack is around 80°, a more obvious low pressure region is formed; When the altitude is 4000m and the operating speed is 360km/h, the negative pressure formed by the roof insulator is equivalent to the air pressure corresponding to the altitude of 4599m. The external insulation correction of the roof insulator shall be considered.