Abstract:In this paper, evolution process of ultrasonic-cavitation bubble in molten steel is about expending、contracting and collapsing of cavitation bubble wall. Through Matlab,t and corresponding R can be solved used by four order Runge-Kutta.Influence of Pa、f、R0 and k on evolution process of ultrasonic-cavitation bubble can be simulated. Results show: There is the threshold value of conversion between transient state cavitation and steady state cavitation with ultrasonic treatment in molten steel. When the value of sound intensity is below or above the threshold value, variations of various parameters can have some different effects on evolution process of ultrasonic-cavitation bubble. In brief, under steady state, through increasing R0, the resonance between ultrasonic and cavitation bubble can emerge used by low frequency, and effects of ultrasonic can be improved obviously. Under transient state, high Pa、low frequency、small R0 and high k(monatomic gas)can improve effects of ultralsonic. In practice of ultrasonic treatment, various parameters can be adjusted to control effects of ultrasonic according to different situation.