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Flashover of ice-covered insulators seriously affects the safe operation of transmission lines. It is necessary to study the electric field distribution for flashover analysis of ice-covered insulators. The electric field of ice-covered insulators was mostly calculated by a two-dimensional (2D) axisymmetric model that cannot be well corresponded to actual icing situations. In this study, a 3D electric field simulation model of ice-covered suspension insulators under moderate icing condition with applied DC voltage was established. Two characteristic parameters, E(av) and E(max) were proposed to measure electric field distortion degree. Based on the simulation results, the effects of water film conductivity, icicle length, icicle deviation angle, and icicle distribution on E(av) and E(max) were studied. The results showed that icicles have a significant influence on the electric field distribution of insulators. E(av) increases with the increase of icicle length and decreases with the increase of icicle deviation angle. E(max) increases with the increase of the icicle length, icicle spacing and adjacent icicle length difference. When the icicle deviation angle is 45°, E(max) is the largest. Lastly, the possible flashover paths were analysed based on the simulation results, which would provide a theoretical basis for building a flashover model of ice-covered insulators.