Abstract: An ultrasonic frequency pulse power supply, applied to the composite ultrasonic frequency pulse arc welding, was designed and developed, and the frequency and amplitude of its output pulse current could be adjusted and controlled independently. A coupling method of ultrasonic frequency pulse power supply with direct current welding power supply was proposed, which is "parallel+auxiliary network". Based on the establishment of control model of output pulse current, the power conversion circuit of ultrasonic frequency pulse power supply was set up, which consists of a buck converter, a full bridge converter and a high frequency coupling transformer. The frequency regulation of pulse current can be achieved by controlling the switching frequency of the full bridge converter, and the amplitude of pulse current was controlled by means of two-stage feedbacks, that is the amplitude adjustment of the buck converter output voltage and the output pulse duty cycle regulation of the full bridge converter, to guarantee its accuracy and stability. The experimental results demonstrate that the frequency and amplitude of ultrasonic frequency pulse current can be adjusted quickly, accurately and steadily, and have a good coupling effect with welding arc.