Abstract: The accumulation of charges on the surface of GIS basin-type insulators under DC voltage can cause electric field distortion, reduce insulation margin, and make the electric field distortion more severe during voltage polarity reversal. The risk of surface flashover and other faults will further increase. Based on the above issues, this paper focuses on the study of downsized basin-type insulators, and uses finite element simulation to study the surface charge distribution characteristics of basin-type insulators under positive voltages, negative voltages, and polarity reversal voltages. Combined with flashover tests, the impact of charge distribution on flashover voltage is revealed. The research results show that the charge density increases with the increase of stating voltage time, leading to a decrease in flashover voltage. Under positive polarity voltages, the maximum flashover voltage can decrease by 9.3%, and under negative polarity voltages, the maximum flashover voltage can decrease by 10.7%. During the transition from negative polarity to positive polarity, the maximum flashover voltage can decrease by 12.3%, while during the transition from positive polarity to negative polarity, the maximum flashover voltage can decrease by 29.4%. Meanwhile, the flashover voltage is negatively correlated with the charge density.