Abstract: The solidification structure and properties of Mg-3Al alloy under graphite mold casting (water cooled at 5 ℃, 1 atm (1.01325×10⁵Pa)) and high-pressure solidification (2 and 3 GPa) were studied by XRD, SEM and EDS. The results show that Mg-3Al alloy is composed of α-Mg at different solidification pressures, but its microstructure changes from equiaxed graphite casting to dendritic clusters under high pressure.The GPa-level high pressure can make the Al solute atoms in Mg-3Al alloy more solidly dissolve into the α-Mg matrix, and at the same time, the solute atoms can also be segregated in the form of interdendritic and grain boundary.The compressive strength and hardness of Mg-3Al alloy at 3 GPa are 372 MPa and 46 HV, respectively, which are significantly higher than those of graphite cast Mg-3Al alloy at 356 MPa and 41 HV.