This study aims to improve the efficiency and accuracy of computer-aided manufacturing (CAM) engineers. A CAM assistant program, which includes the tool-path planning, cutting tool database, and cutting chatter modules, was developed using the application programming interface (API) provided by Siemens CAD / CAM software NX. The module of tool-path planning can recognize processing parts to decide suitable operation and corresponding processing strategy for the part, which is essential to generate the cutting tool-path. The module of cutting tool database is connected to a MySQL database, in which the suitable cutting parameters of each cutting tool for different materials are saved. The parameters are obtained from the cutting tool manufacturers or the users who conducted abundant machinability tests. The module of cutting tool database can help CAM engineers to extract the correct cutting parameters from the cutting tool database. In addition, the module of cutting chatter includes the stability lobe diagrams, which can be used to determine the cutting stability of the machining parameters. The stable area shown in the stability lobe diagram is the range of cutting parameters which would not introduce chatter. It can be used to compare with the original designed machining parameters and adjust the parameters into stable range. With the developed modules in this study, it is expected to reduce the time to design NC programs and to improve the reasonability of the cutting strategy. Furthermore, the productivity will be increased.