Abstract: Filled with micro-Al₂O₃(0.5~3 μm), micro-Si₃N₄(0.3~3 μm) and nano-Al₂O₃ , different thermal conductive silicone rubber composites were prepared by the blending method. Micro-Si₃N₄ and nano-Al₂O₃ according to different volume ratio were compounded with silicone rubber and the total volume fraction was fixed at 30%. It is found that with the same volume fraction, the thermal conductivity of all the micro-Si₃N₄ and nano-Al₂O₃ co-filled composites have remarkable improvement compared with that of the composite filled with micro-Si₃N₄. Especially, when the volume ratio of micro-Si₃N₄ to nano-Al₂O₃ is 26∶4, the thermal conductivity (1.64 W/(m·K)) is three times as high as that of the composite filled with micro-Si₃N₄ (0.52 W/(m·K)). At the same time, the micro-Si₃N₄ and nano-Al₂O₃ co- filled silicone rubber composites remain the good voltage breakdown strength and excellent insulating properties.