In order to reveal the mechanism of the contamination depositing on the surface of the roof insulator under the high speed flow, the particle collision number was used to describe the contamination depositing characteristic in this paper, and the effect of particle size and wind speed on contamination depositing was analyzed. In sandy area, asymmetry of friction makes the particles charged, and the trajectories of charged particles under the electric field were carried out. The results show that the faster air velocity, the greater particles diameter, the more serious contamination depositing; when the contamination particles are charged, the contamination depositing characteristic on the surface of the insulator changes little. As for this result, a hypothesis was proposed after the analysis and calculation, and finally this hypothesis was proved to be right through the simulation.