Abstract: With assumption that the lubricant is a mixture of fluid and bubble nuclei and its distribution is homogeneous, we introduce a dynamic model of cavitation and couple it with Reynolds equation of hydrodynamic lubrication of plain bearings. The model under lubrication state is sovled with numerical simulation. Euler method, a 4-5th order Runge-Kutta method and a finite difference method are used to explore effect of initial gas content on axis trajectory and lubrication characteristics.