Corner radius end mill, whose cutting capability is mostly affected by the relief surface, is a kind of highly effective end mill . So a novel mathematical model of relief surface curve about corner radius end mill, which is verified with a five-axis computer numerical control (CNC) grinding machine and simulated based on a system CAM, is derived and presented in the paper. According to the proposed tool coordinates system and the mechanical coordinate of the machine, the relative motion between the cup wheel and the tool is determined. In order to obtain an accurate relief curve when machining, the model of a cup wheel edge is also introduced. The coordinates of grinding point when grinding relief surface are calculated. With the input data of the corner radius end geometry, wheels geometry, wheel setting and machine setting, the NC code is generated automatically from the program. Then the code is used to simulate in 3 Dimension before actual machining. Finally, the NC code will be used for machining in the CNC grinding machine. The roundness of the round corner in the final product is very well, means this model is effective.