Epoxy　resin　is　widely　used　as　insulating　materials　in　the　electric　power　equipment;　however,　these　properties　are　affected　by　the　dielectric　relaxation　greatly.　In　this　paper,　three　kinds　of　E51　bisphenol　A　epoxy　resin　with　different　epoxides　were　used　to　make　samples　for　differential　scanning　calorimetry　experiment,　fourier　transform　infrared　spectroscopy　test　and　broadband　dielectric　spectroscopy　experiment　to　research　the　effect　of　epoxide　on　molecular　chain　relaxation.　The　results　demonstrate　the　relaxation　of　molecular　chain　determines　the　complex　permittivity　at　high　frequency　when　the　temperature　is　over　glass　transition　temperature　Tg).　Through　fitting　the　complex　permittivity,　it　is　found　the　molecular　chain　relaxation　of　epoxy　is　dipole　relaxation　polarization.　Epoxy　resin　with　higher　epoxide　has　stronger　polarization　intensity.　©　2021　IEEE.