Abstract: Since conventional ultrasonic is inconvenient for application during welding process, a new method to emit ultrasonic has been proposed. With the addition of modulating signal to the TIG welding loop by the high-frequency power electronic switch inverting techniqUe, the arc-ultrasonic has been excited corresponding to the rising-edge and the descending-edge of the modulating electronic current. The amplitude of the signal recorded by the microphone is linearly proportional to the current if the based current is modulated by a small amount. The signals corresponding to the rising-edge and the descending-edge of the modulating electronic current can be separated if the pulse width of the modulating signal is big enough. The experimental results show that the V/I character of the modulated are is much more disordered. The mechanism of the arcultrasonic generation and some characters of the arc-ultrasonic are discussed by the wave eqUation and by the physical property of the modulated arc. The arc-excited ultrasonic has more advantages of controlling welding process and improving the quality of the weld in engineering.