Based on the modal analysis of the finite element model (FEM) of the machine bed, the position of the modal strain energy concentration in the first mode is selected, and the sensitivity analysis method is used to optimize the design size of the bed. The optimization results show that the first-order modal strain energy can be distributed evenly after optimization, and the quality of the bed can be reduced. At the same time, the blindness of structural optimization can be reduced and the optimization efficiency can be improved. This optimization design process and method can be extended to other machine tool parts, and provide the important approach and theory reference for machine tool dynamic characteristics improvement and structure optimization.