Abstract: The effect of Si coated on the graphite surface and the grain diameter of graphite flake on thermal and mechanical properties of graphite/Al composites was researched. The results show that the SiC layer is formed during coating process, which is beneficial to suppress the formation of Al₄C₃ phase and enhance the interface bonding. The thermal conductivity in X-Y plane direction of the graphite-Si/Al composite increases from 492 W/(m·K) to 654 W/(m·K) as the volume fraction of the graphite increases from 50vol% to 70vol%. The flexure strength of graphite/Al composites with 50vol% graphite approachs 81 MPa, which increases by 53% than that of the uncoated graphite/Al. The thermal conductivity in X-Y plane direction of graphite-Si/Al composite decreases from 654 W/(m·K) to 445 W/(m·K) with the grain diameter of the graphite decreases from 500 μm to 150 μm. However, the thermal conductivity in Z plane direction and the flexure strength exhibit no significant change.