A three-dimensional hydrodynamic lubrication model based on lubrication theory is developed which accounts for pad roughness and slurry flow. The distribution of the slurry film thickness and pressure between the pad and the wafer are predicted using the model. The effects of the pad roughness, the polishing applied load and rotation speed on slurry film thickness and tilt angle are discussed. At last, a CMP experiment is carried out. It is found that the results are proved the three-dimensional model considering pad roughness agrees well with our experimental data. The results improve the previous models so that the CMP process can be better simulated using the model. Furthermore, they are useful in the processing of CMP and the design of the pad roughness.