To order for quick and easy prediction and optimization of energy efficiency in different stages of the service process of machine tool, a machine tool service process calculation model of energy efficiency was established based on milling characteristics, which mainly included Startup, noload and processing of three stages. This process was mainly composed of auxiliary and processing efficiency. By accessed to the corresponding correction coefficient through the analysis of experimental data, the machine tool energy consumption of each stage was calculated by the established mathematical model. The energy efficiency at each stage was the ratios of that energy consumption to the total input energy consumption. Finally, the experiments of study are conducted on a CNC milling machining center, and the results demonstrate the accuracy of the calculation method, so the calculation model can be applied to machine tool efficiency evaluation and prediction. 