The structure finite element model for the working device of hydraulic excavator was established, and each order modal frequency and modal characteristics of working device were gotten by analyzing the free mode of the finite element model. The key modal frequency was determined, which influenced the dynamic performance of the working device, and taking the key modal frequency as the optimization goal the sensitivity analysis was conducted for the main structural parameters to set up the dynamic optimum design variables of working device. Taking the geometric constraints and performance constraints of work device as constraint conditions, the dynamic optimization design was conducted by using augmented Lagrangian method. The instance analysis showed that the structure stiffness was improved, and the structure deformation was reduced. And the dynamic working performance and the structure stability reliability for the working device were improved.