Pollution distributes irregularly on the surfaces of traction power supply system insulators as high-speed trains pass through pollution aerosols. This affects the flashover characters. Insulator polluting characteristics were studied in a wind tunnel at speeds up to 100 m/s. The gas-solid aerosol flow around insulator was analyzed and a pollution accumulation model was established after analyzing the forces on dust particles. Additional simulation shows that with the aerosol velocity increases, pollution accumulates more on the windward side and leeside. Accumulation on the leeside increases as the crosswind side decreases. When viscosity and pollution density are constants, the quantity of pollution on upper surface of a post-type third-rail insulator shed is not so uniform, but has maximum and minimum values. This numerical modeling result corresponds well with experiment. A method is proposed to express the pollution distribution using ESDD and NSDD.