Recent studies have shown that the collapse of cavitation bubbles in a jet pump can generate an extremely high pressure with many potential applications. The dynamics of the bubble is goved by the Rayleigh-Plesset equation. With the bubble dynamics equation and the heat and mass transfer model solved with the Runge-Kutta fourth order adaptive step size method, the oscillations of the bubble in the diffuser of the jet pump are assessed under varied conditions. To obtain the pressure variation along the diffuser, the Boulli equation and the pressure measured in experiment are coupled. The results of simulation show that a transient motion of the bubbles can be obtained in the diffuser quantitatively, to obtain the pressure and temperature shock in the bubble.Moreover, increasing the outlet pressure coefficient would result in a more intense bubble collapsing process, which can be used in the subsequent studies of the cavitation applications. The predictions are compared with experiments with good agreement.