The oil film stiffness of hydrostatic thrust bearing has a significant influence on the accuracy and stability of the computer numerical control (CNC) vertical machining equipment. A theoretical stiffness model for multi-pad sector cavity bearings was established based on hydrodynamic lubrication theory, employing a combined theoretical and experimental approach, aiming to explore the influence of lubricating oil viscosity, worktable rotational speed, and load on the oil film stiffness. An experimental platform with oil film thickness sensors was developed to validate the model under variable rotational speeds (5–40 rpm) and axial loads (0–10 t). The experimental results showed that under no-load conditions, increasing the rotational speed from 5 rpm to 40 rpm could reduce the oil film thickness by 9.5% (from 243 µm to 221 µm). Notably, under a 10 t load, the oil film thickness decreased by 41% compared to no-load conditions at identical rotational speeds, with stiffness values increased by a factor of 1.7. Theoretical predictions identified closely with experimental data, exhibiting a maximum relative error of less than 8%, which confirmed the accuracy of the theoretical stiffness model. These findings provided a theoretical foundation for optimizing the design of hydrostatic thrust bearings and improving the machining accuracy and operation stability of vertical CNC equipment.