Evolution of microstructure and precipitation process of 40%SiC p /Al–20Si composite solidified under high pressures were investigated. The results demonstrate that undissolved Si phase under 1GPa is much smaller than 0.02GPa, and disappears under 2GPa. Primary α-Al phase appears at 1GPa, and with increased pressure, more primary α-Al phase emerges. Eutectic silicon phase is modified effectively under high pressures. A supersaturated Al(Si) solid solution is obtained. GP zones form in primary α-Al phase when solidified under 3GPa and nature aging for 400days. Dispersed and fine Si phase precipitates by manual aging at 209°C.