Spheroidization and non dendritic A356 semi-solid slurry was prepared using power ultrasonic double vibration heads device, then the slurry was used in rheological die forging. The different positions of forgings metallographic structure were compared. The results show that the grains of upper and bottom are small; the grain of central part is coarse where the liquid phase is less than margin. The internal motion process of semi-solid slurry under the condition of the pressure was analyzed. The forgings mechanical performances at pouring temperature of 640 ℃ with and without power ultrasound treated were studied, which show that the treated one is better.