Abstract: Epoxy resin is widely used in the electrical industries because of its strong adhesion and excellent insulating properties. However, the low thermal conductivity of epoxy resin limits its application, especially in a high-frequency condition. In this paper, the thermal conductivity and electrical insulating property of the epoxy resin composite were studied by filling the epoxy resin with the micro-nano binary filler prepared by dopamine modified micro-BN and nano-Al₂O₃. The results showed that the thermal conductivity of 22.5 wt% BN and 7.5 wt% Al₂O₃ composite could reach 1.35 W/(m·K), which was 812.5% higher than that of neat EP, while the dielectric loss was kept at a low level. The results of high frequency breakdown experiments showed that the breakdown time of the composite was significantly increased, which was 38.7% higher than that of neat EP. The composite prepared by this method has the advantages of high thermal conductivity, low dielectric loss, high frequency breakdown strength, providing a reference for the development of thermally conductive but electrically insulating materials for high frequency power electronic equipment.