Abstract: In order to understand the ultrasound-MIG welding process better, the droplet transfer behavior during ultrasound-MIG welding of aluminum alloy was investigated in this paper. Through observation and analysis of the droplet transition process and electrical, the results show that droplet is hampered by the effect of ultrasound radiation force, the volume of the droplet increases, and the transition frequency is reduced in short circuiting transfer form; the frequency of droplet transfer increased significantly and the size of the droplet decreases due to the effect of ultrasound radiation force in globular transfer and spray transfer. And the effect of ultrasound makes the droplet shape changes more frequently, the instability of the welding process is increased.