Abstract: The effects of high-power and long-time ultrasonic melt treatment on the microstructure and properties of hypereutectic Al-17Si and Al-24Si alloys were studied by means of metallographic microscope (OM) and Brinell hardness tester. The results show that the high-power and long-time ultrasonic melt treatment can refine the silicon phase in hypereutectic Al-Si alloys and make the distribution more uniform. When the ultrasonic temperature is at the liquidus temperature, the ultrasonic refining effect is the best, which can improve the distribution uniformity of silicon phase and the hardness of hypereutectic Al-Si alloys. The hardness of Al-17Si alloy and Al-24Si alloy after ultrasonic treatment reaches 55.2HB and 60HB, increasing by 3.5%and 8.7%respectively.