Abstract: The effect and mechanism of ultrasonic vibration of diverse frequencies on the degassing of 7050 and 1060 aluminum alloy melt at different temperature ranges were studied through the detection of hydrogen content by HYSCAN-II apparatus. The results show that the hydrogen content of the melt treated by ultrasound is evidently reduced; the hydrogen content of the melt increases as the temperature increases; while the temperature of metal liquid heightened from 660 to 720°C, this effect is slow down, but the degassing efficiency changed little; both the efficiency and effect treated by ultrasonic vibration of 15 kHz frequency are better than that of 20 kHz frequency. The cavitation effect caused by ultrasonic vibration creates plenty of cavitation bubbles. These bubbles can absorb and carry away the hydrogen in metal liquid when they grow up and collapse. Vibration frequency plays a decisive part in cavitation bubble growth and the diffuseness of hydrogen in metal liquid.