Curved surface parts are widely used in aerospace industry, automotive industry and other fields due to their excellent features in aerodynamics, fluid dynamics and thermodynamics. Compared with the modeling technology of the curved surface, the development of the processing technology of the curved surface is slightly behind. In order to improve the processing quality and efficiency of the curved surface, this paper independently developed a five-axis CNC polishing machine tool, and studied the pre-processing and the post-processing when machining the curved surface. Taking a metal shell of the mobile phone as an example, three different paths are planned for the flat surface and the curved surface respectively, and a method for generating the tool path is proposed. The kinematics model of the five-axis CNC machine tool is established, which is used to obtain the calculation formula of the movement amount of each axis when polishing in the flat surface and the curved surface of the metal shell. The polishing effects of the different paths about the surface quality and the polishing efficiency of the metal shell are studied through the polishing experiments, and the polishing path with the best surface quality and the highest polishing efficiency is found.