Abstract: Underwater wet welding usually accompanied poor arc stability, arc blowout, nonuniform weld appearance and other problems. Ultrasound-assisted underwater wet welding method was developed to solve these problems. Its principle is to use the ultrasound combined with common underwater wet welding to improve welding arc stability, weld appearance and the weld quality. Bead-on-plate welding experiments were carried out with the ultrasound-assisted underwater wet welding equipment. The results showed that ultrasonic can improve the weld appearance and stability of welding process. The arc blowout rate is obviously decreased, the weld penetration is increased, and the reinforcement is decreased. The micro-hardness of the central weld is also decreased.