The flashover of post insulators in rainy weather is an important factor affecting the safety of the power grid. For the insulator in operation

installing water-cut sheds is the most effective measures to improve the anti-rain flashover ability. To explore the selection method of water-cut sheds’ parameters

this paper uses the finite element method to establish a composite post insulator model with water-cut sheds to study the electric field distribution influenced by the number of sheds and the overhangs. The field strength of the surface of the sheds and the field strength of air gap were proposed as the criterion for selecting water-cut sheds parameters. The results show that installing water-cut sheds will make the field strength of the air gap between the nearby big sheds and the nearby small sheds stronger

and water-cut sheds’ field strength will be stronger. According to the relationship between the field strength of surface and air gap

using the electric field of air gap as the criterion is recommended. This paper has certain guiding significance for the installation of water-cut sheds and the measures of preventing wet flashover.