Hydrostatic slideway is a key part for the heavyduty gantry CNC machine, which supports the total weight of the gantry and moves smoothly along the table. Therefore, the oil film between sliding rails plays an important role on the carrying capacity and the precision of machine. In this paper, the oil film without friction is simulated by 3D CFD model. The carrying capacity of heavy hydrostatic slideway, pressure and velocity characteristic of the flow field are analyzed. The simulation results have been verified by comparing the experimental data obtained for the heavyduty gantry machine. For the requirement of engineering, the oil film carrying capacity is analyzed with simplified theoretical method, and the machining precision is evaluated and the effectiveness is verified by the experimental data. The simplified calculation method is proposed to design the oil pad on heavyduty gantry CNC machine hydrostatic slideway.