A frequency control method and system for an ultrasonic surgical tool. The frequency control method for an ultrasonic surgical tool comprises: obtaining a maximum value of a phase difference between an operating voltage and an operating current of the ultrasonic surgical tool (101)； determining whether the maximum value is less than zero (102), so as to obtain a first determination result； if the first determination result indicates that the maximum value is not less than zero, adjusting an operating frequency of the ultrasonic surgical tool to a frequency corresponding to the phase difference equaling to zero (103)； if the first determination result indicates that the maximum value is greater than zero, subtracting a preset value from the maximum value to obtain a phase lock-point (104)； and adjusting, according to the phase lock-point, the operating frequency of the ultrasonic surgical tool (105). The frequency control method for an ultrasonic surgical tool solves a problem in which, in some situations where the phase of a self-resonant frequency does not exceed 0, ultrasonic surgical tools fail to operate normally, or operate inefficiently, thereby improving operation efficiency and stability of ultrasonic surgical tools.
