Epoxy resin is one of the primary insulating materials used in high-voltage power equipment due to its excellent insulating properties. This paper investigates the DC conductivity and thermal conductivity of Al2O3/EP composites with 0wt%, 0.5 wt%, 1.0 wt%, and 2.0 wt% Al2O3 content. The experimental results indicate that the conductivity of Al2O3/EP composites increases nonlinearly with the rise in electric field strength, with the optimal performance observed at 2.0 wt% Al2O3 content. Additionally, the thermal conductivity of EP composites gradually increases with the addition of Al2O3. As the temperature increases, the DC conductivity of the 2.0 wt% Al2O3/EP composite also increases. The thermally stimulated current (TSC) test reveals that this is due to the higher carrier concentration at elevated temperatures, which enhances the transport capability of carriers and thereby increases the DC conductivity of the EP composite. The findings of this study provide new directions for the research of novel materials.