Abstract: On the basis of variational design technology based on FEM and its application in static and dynamic structure designs, the concepts of structural quasi-static property and variational design were stated, and as an example, the structure of a hydraulic machine was optimized using the quasi- static variational optimization design. In addition, the method of improving its dynamic properties by the dynamic optimization of element structures was proposed. Finally, the general principle and method of dynamic optimization design of mechanical structures were discussed.