In this study, geometry model for efficiency evaluation and demonstrate qualitative and quantitative analysis are established by utilizing differential geometry. Based on the machining conditions of the uses of flat end cutter (FC) and disc cutter with a concave end (DCC) in the numerically controlled (NC) machining process, this study aimed to establish a related geometry model for efficiency evaluation and demonstrate qualitative and quantitative analysis by utilizing computer modeling. The analyzed parameters such as efficiency, accuracy and economical utility for different machined surfaces will be reported to provide reliable selection criteria of FC and DCC in order to improve NC machining.