Epoxy　resins　are　susceptible　to　be　eroded　by　hydrothermal　environment,　which　causes　deterioration　of　insulation　performance,　and　directly　impairs　the　safety　and　stability　of　power　system　operation.　In　order　to　clarify　the　change　trend　of　the　dielectric　properties　of　epoxy　resin　materials　in　hydrothermal　ambience,　artificial　hydrothermal　aging　experiments　were　conducted　on　cured　epoxy　resin　samples　to　investigate　the　effect　of　aging　temperature　on　its　electrical　properties,　and　the　aging　mechanism　was　analyzed.　The　experimental　results　indicate　that　the　mass　of　epoxy　resin　samples　will　augment　due　to　moisture　absorption　after　hydrothermal　aging.　Plasticizing　effect　of　water　molecules　on　the　epoxy　resin　matrix　will　lower　its　glass　transition　temperature.　The　volume　resistivity　of　epoxy　resin　samples　will　decrease　after　exposing　to　hydrothermal　ambience,　while　the　relative　permittivity　and　dielectric　loss　factor　will　increase　especially　in　the　low　frequency　region.　The　AC　breakdown　phenomenon　of　epoxy　resin　samples　is　explained　using　Wagner＇s　thermal　breakdown　theory,　and　the　power　frequency　AC　breakdown　strength　of　epoxy　resin　will　decrease　due　to　the　increase　in　relative　permittivity　and　dielectric　loss　factor.　Higher　aging　temperature　can　promote　the　hygroscopic　process　of　the　epoxy　resin,　which　will　increase　the　moisture　content　in　equilibrium　state　and　cause　the　dielectric　properties　to　further　decrease.　©　2021,　High　Voltage　Engineering　Editorial　Department　of　CEPRI.　All　right　reserved.