Epoxy resin (EPR) insulations play a vital role in the insulation of modern power electronic equipment owing to their excellent dielectric properties. However, due to the high‐power density and miniaturization of power equipment which causes high heat fluxes under high voltage and high‐frequency stresses, EPR with good thermal and insulation properties is urgently needed. In this study, the polydopamine functionalized micro‐BN and core‐shell nano TiO2–SiO2 particles are dispersed in EPR to simultaneously improve thermal and dielectric insulation properties. It is revealed that the addition of micro‐nano particles significantly improves the thermal and dielectric performance. Particularly, the high thermal conductivity of micro‐BN and the dielectric barrier effect due to the core‐shell structure of nano TiO2–SiO2 are the main reasons for improved thermal and dielectric insulation performance, respectively. The EPR composite containing 3 wt% of micro‐BN and 1 wt% of nano TiO2–SiO2 exhibits the optimal performance with 0.49 W/mK thermal conductivity and the highest dielectric strength among all the samples, that is, 60.61 kV/mm even at 10 kHz and 90°C. This study found that the crucial factors are the surface encapsulation, weight percent, and homogeneous dispersion of particles in EPR, the dielectric barrier effect, thermal conductivity, and the mismatch between the dielectric constant of EPR and particles. This study proposes the optimal weight percent of suitable micro‐nano particles for EPR to produce suitable composites for high‐frequency and high‐temperature applications. Enhancement mechanism of thermal conductivity and dielectric breakdown strength.