Abstract: Using the mixture model and the cavitation model of Fluent, the ultrasonic cavitation effect and cast microstructure at different ultrasonic powers for 7050 aluminum alloy melt was simulated, and then was analysed through casting experiment with ultrasonic treatment(UST).The results show that the cavitation region in melt expanded gradually with the increase of the ultrasonic treatment time, and concentrated on the center of horn surface gradually. The higher the ultrasonic power and cavitation strength were, the refiner the microstructure was.The simulated results matched the experimental results.