Abstract: Industrial aluminum melt was treated by ultrasonic vibration above liquidus temperature.The effects of ultrasonic powers,melt temperatures and depths of applying vibration with continuous ultrasonic processing on solidification microstructure were studied.The effects of dynamic intermittent vibration on solidification microstructure were also analyzed.The results indicate that the microstructures of ingot casting through ultrasonic vibration were all refined to different extents.Mechanism of ultrasonic grain refinement is mainly due to cavitation and acoustic streaming effects which increase nucleation rate and inhibit the growth of crystal.Grains can be most effectively refined with applying reasonable ultrasonic power and melt temperature during the ultrasonic proces.The depth of applying vibration should not be too deep,otherwise it will weaken the refining effect.Grain refining degree relates to parameters selected under different conditions of dynamic intermittent vibrations.