A new method of NC machining simulation based optimization of cutting parameters is proposed. For the case of NC turning process, the method of extracting cutting parameters from NC programs is given. Based on the cutting theories, using linear weighted method, the multi-objective optimization function is constructed, and it is solved by complex method. The modification and storage strategy of parameters is also given. The application shows that the proposed method cannot only ensure the accuracy of NC code, but also provide the optimized cutting parameters under the constraints of appointed machine tools. It will be helpful for the optimization and intelligence of NC machining.