Abstract: Semisolid ZL101-La Al alloy slurry is prepared by ultrasonic vibrating. The effects of processing parameters of ultrasonic vibrating such as ultrasonic power, melt temperature and treated time of ultrasonic vibrating on primary phase of the alloy are researched. The results indicate that it is feasible for ultrasonic vibrating combining RE to prepare semisolid ZL101 Al alloy slurry, and the ultrasonic power is the main factor affecting morphology of primary phase in the alloy. The suitable preparing parameters are obtained by the orthogonal design, in which the power of ultrasonic vibrating is 150 W, the melt temperature is 650 ℃, and the ultrasonic treated time is 30 s.