Al₂O₃/Al-10Si composites were prepared by high pressure solidification at 3, 4, 5 GPa, and then heat treated at 160 °C for 2, 4, and 6 h. Thermal stability of microstructure and mechanical properties of Al₂O₃/Al-10Si composites under high pressure were systematically studied. The results showed that heat treatment leads to the precipitation of Si particles due to the supersaturation in α phase.The precipitation of Si leads to a decrease of supersaturation. The compression strength and ration shows a slight increase after heat treatment due to the combination of precipitation strengthening and solid solution strengthening. At 160℃/4h, Al₂O₃/Al-10Si composites showed the best mechanical properties. After solidified under 5GPa and heat treatment at 160℃/4h, Al₂O₃/Al-10Si composites got the maximum compressive strength which is about 716MPa.