In order to effectively solve the problems of difficult planning of NC machining of complex surfaces and high requirements for users’ NC machining knowledge and experience, a decision-making system for milling methods was designed based on NX CAM software to meet the needs of finishing machining of complex surfaces.The system could extract the machining features associated with specific machining methods in complex surfaces, and reasonably selected one of the four main milling methods for processing complex surfaces: depth contour milling, fixed axis contour milling, hybrid milling, and variable axis contour milling. The secondary development method combined with NX Open C (UFUN) and NX Open C++ was used for example verification. The results show that the system can reduce the process of human-computer interaction, reduce the technical requirements for programmers, and reduce the time of NC programming to a certain extent.