The invention discloses a dynamic matching device of an ultrasonic power supply and a method thereof. The dynamic matching device comprises an ultrasonic signal generator, a driving isolating circuit, an ultrasonic power amplifier, a matching transformer, a tuning inductor and an ultrasonic transducer which are successively in serial connection, and further comprises a voltage and current sampling circuit, wherein the voltage and current sampling circuit is successively connected through a backward stage isolating circuit, a filter shaping circuit and a programmable logic device (PLD), a phase measurement unit is arranged in the PLD, and a pulse width modulation (PWM) drive pulse output end of the PLD is connected with the ultrasonic signal generator. According to the dynamic matching device and the method thereof, frequency of ultrasonic driving signals is dynamically regulated through real-time monitoring of the impedance characteristic of an ultrasonic transducer circuit, a dynamic matching process is achieved, the fact that the transducer works on a resonance point all the time is guaranteed, the maximum available power is outputted, matching precision is high, the circuits are simple, achieving cost is low, achievement is easy, and a wide application prospect is provided.