Abstract: Using particle image velocimetry (PIV) experiments and CFD numerical simulation, the flow characteristics of the oil cavity in the hydrostatic support system of high-end CNC machine tools have been investigated. The influences of inlet Reynolds number (Re), oil cavity depth (H) and clearance height (h) on vortex structures, wall pressure and shear stress distribution in the oil cavity have been studied. The results show that the simulation results agree well with experimental results. There exist complex vortex structures in oil cavity. The vortices number varies from one to three and the vortices size and positions change as Re (70~1400) increases. The vortices size increases and vortices number decreases as H varies from 6mm to 18mm. As h increases, the vortices size increases obviously. The wall pressure and shear stress increase as Re increases and h decreases in the same conditions. The results provide a foundation for improving the stability and carrying capacity of hydrostatic oil cavity.