Abstract: This paper presents a method of dynamic optimization of machine tool structure based on energy balance principle. The dynamic performance of machine tool is improved by improving the uniformity of energy distribution of machine tool parts. Taking the dynamic performance optimization design of gantry of CNC engraving and milling machine as an example, this method is expounded in detail. The paper firstly uses modal analysis in finite element analysis software to find the dangerous modal, secondly identifies the concentrated area of the kinetic energy and potential energy distribution, then optimizes the part structure on the principle of energy balance, finally evaluates the uniformity of energy distribution by standard deviation. The results prove that the dynamic performance of machine tool is improved by the better uniformity of energy distribution.