The invention relates to a frequency searching and controlling method of ultrasonic biological treatment. In the method, a wide frequency domain ultrasonic power device is utilized, and an operation policy with an optimal treatment frequency is searched, caught, controlled and locked by adopting a multi-band treatment sequence. During operating, in the working frequency domain of the ultrasonic power device, an energy converter, an amplitude transforming rod and a (tool head) vibrator which are matched with a central frequency of frequency bands are sequentially arranged along a frequency band frequency searching direction; through coordinating and controlling by a control (master control, display and operation parameter setting functions and frequency scanning mode and power given functions) terminal, synchronous frequency scanning is carried out on an upper limit frequency definition frequency band and a lower limit frequency definition frequency band; and by taking the natural frequency of the energy converter as a reference, the upper limit frequencies and the lower limit frequencies of all the frequency bands and the scanning modes can be manually set and also be automatically and continuously connected, thus various biological cells, article surface stains, pollutions and dirt can receive ultrasonic actions with a proper frequency and are locked on the frequency so as toimprove the treatment efficiency in multiples.