In this study, simulation based on a theoretical model was made to investigate the influence of inertial effect and friction force to CNC machine’s accuracy and to explore the functions of related control parameters. By using empirical method, an auto-tuning system that can on-line tune the CNC control parameters based on the detected weight of workpiece was developed. In addition, an on-line weight identifying system was also developed. After integrating the two systems, an intelligent parameter-tuning system which can be directly implanted into CNC controller was developed. Experimental results have shown that the system can effectively improve the accuracy of a machine tool through on-line control parameter tuning.