Under the action of a single wind direction, more contamination accumulates on the leeward side of the insulator in service, which reduces its insulation performance. The movement of charged pollution particle was simulated by establishing a three-dimensional coupling model, revealing that the backflow and eddy flow on the leeward side of the insulator are the main reasons for pollution accretion. The manual coating method was used to simulate non-uniform pollution on the windward / leeward side, and AC flashover tests were conducted to investigate the effects of average salt density (SDD), salt density ratio (J) between the windward and leeward sides, and leeward area ratio (R) on the average flashover voltage (Uf ). The results show that Uf decreases with the increase of SDD, and increases with increasing J and R. Moreover, J has a stronger impact on Uf under the small values of SDD and R. While R imposes a greater effect on Uf when SDD and J are low. By observing the flashover process of polluted insulator, it was found that the arc develops randomly when uniformly polluted, while the arc always propagates along the leeward side under non-uniform pollution, and the amplitude of the leakage current is larger during the voltage increment.