The current power ultrasonic technology has been widely applied. In actual machining, the working condition of vibration realization device transducer depends on the magnitude of the external load impedance and the temperature change of the transducer during the machining process. The resonant frequency of the transducer will also change, resulting in a mismatch with the output frequency of the generator, which will have a negative impact on the output amplitude and processing efficiency of the transducer. In order to obtain the rule, design theory of transducers, simulation and test methods were used to investigate the effects of the external inductor at light loads the resonant frequency of the transducer the influence of external inductance on the resonant frequency of the transducer under light load. The results show that the resonant frequency of the transducer increases with the increase of the length of the transducer horn into the water. By switching in a tuning inductor, the resonant frequency of the transducer will be compensated by a certain amount, so that it can be returned back the preset frequency value. As the value of external inductor increases, the resonant frequency of the transducer will decrease. It is concluded that the use of inductive load can effectively solve the frequency drift caused by the external load of the transducer.