It is one of most important techniques for monitoring and assessing the energy efficiency of CNC machine tools. Conventional methods usually need install a force/torque sensor to indirectly measure cutting power, which are not only increase cost but also influence machine tools’ stiffness. A new method was proposed that the cutting power was estimated directly from the input power without measuring the cutting torque or cutting force. The additional load loss power function of the main drive system was established by experiments.Then, cutting power was calculated based on the additional load loss coefficient. Three experiments were undertaken on a CNC lathe CJK6136 to verify the proposed method.The experimental results show the effectiveness of the method and the estimation error of cutting power is about 1%.