Abstract: Alicyclic epoxy insulators are expected to be widely used in transmission lines because of their excellent electrical properties and good interfacial bonding ability between core rods and sheaths, which effectively solves the interfacial problem of the early silicone rubber composite insulators. At present, there is a lack of comparative studies on the water absorption aging characteristics of the interfaces between the rods and housing in composite insulators made by the epoxy composite insulator and the silicon rubber. This paper compares the water absorption, dehydration, water permeability and moisture permeability of the alicyclic epoxy resin material and the silicone rubber material. The water diffusion test proved that the alicyclic epoxy resin insulator has a better mandrel-sheath interface bonding and aging resistance. Meanwhile, the influence of the ATH filler on water absorption and seepage characteristics of the epoxy resin is studied, which provides a theoretical support for determining the ATH particle sizes and the additive amount in the formulation of the alicyclic epoxy resin for the insulators.