Abstract: In order to obtain the contact pressure distribution and its effect on the flatness of the silicon wafer in the chemical mechanical polishing process, the mechanical and mathematical models were developed from the aspect of practical application. The contact pressure distribution was calculated and analyzed with ANSYS, and then confirmed by polishing experiments. The contact pressure distribution and how it was affected by the parameters of a polishing pad were obtained, and the relationship between the non-uniform distribution of the contact pressure and the flatness errors of the polished silicon wafer was determined. The results show that the contact pressure distribution is non-uniform, with the maximum pressure occurring on the edge of the silicon wafer, which induce the flatness errors and the edge subsiding. Selecting Young's modulus and Poisson's ratio of the polishing pads properly can improve the uniformity of the contact pressure distribution and the flatness of the functional region of the wafer.