Abstract: Ultrasonic field was introduced into the solidification process of industrial pure aluminum. The mechanism of grain refinement by ultrasonic was discussed. The effects of ultrasonic power and melt temperature range subjected to ultrasonic vibration on the solidification structure of casting ingots were studied. The experiment results showed that the solidification structures of aluminum melt were all refined remarkably by ultrasonic treatment due to ultrasonic cavitation effect and acoustic stream effect. The structure refinement was improved when the ultrasonic power increased, the refining effect was the best at the ultrasonic power of 170 W, but it would be decreased if the ultrasonic power continuously increased. The similar law was found in investigating the influence of temperature range applying vibration on the solidification structure, and the grain refinement can reach an optimum degree at a reasonable temperature applying ultrasonic.