Microstructure and micro-mechanical properties of LC4 aluminum alloy were studied before and after treating the samples at 4 GPa pressure. The hardness, elastic modulus and plastic deformation were measured by nanoindenter and the microstructure of the LC4 aluminum alloy was observed by metalloscope and scanning electron microscope. The results show that the microstructure of the LC4 aluminum alloy can be refined and compacted after 4 GPa pressure treatment. The micro-mechanical properties of LC4 aluminum alloy can be improved effectively.