Abstract: The analog power supply of ultrasonic welding has the shortages of inaccurate frequency tracking and unadjustable amplitude in the process of welding, which make the welding process unstable, sometimes even lead to failure.The design scheme based on digital signal processor(DSP) was proposed to improve the reliability and stability of ultrasonic metal welding.Frequency tracking was realized by using incremental PI algorithm through gathering phase difference signal between voltage and current of piezoelectric transducer(PZT).The method of pulse width modulate(PWM) was used to control and adjust the amplitude of ultrasonic vibration.The results indicated the ultrasonic welding power supply based on DSP could adjust the amplitude continuously and track the resonant frequency in 0.32 ms during the welding process.