Abstract: In order to investigate the mechanism of cavitation in an inner hole rotary cavitation generator, a numerical method was proposed to analyze the effect of different hole structures on the cavitation flow. Results show that when the pressure was reduced to the saturated vapor pressure of the water, cavitation will occur in the hole. Due to the high speed rotation of the rotor, there exist significant mass transfer between the water and vapor. The structural parameters of the cavitation generator, the depth <i<L</i<, diameter <i<D</i< and inclination angle <i<α</i< of hole directly affect the cavitation area and the transfer process between water and vapor. At a certain speed, an optimum value of the structural parameters exists. Under the condition of rotational speed of 2 850 r/min, the cavitation area and the transfer process between water and vapor seems more significant when the inclination angle of hole is 30 degree, the diameter is 23 mm and the depth is 35 mm.