To improve dynamic performance’s optimization efficiency of hydraulic excavator’s work device, the dynamic modification simulation of the structure was investigated by dual modal space method based on modal analysis. The results show that the mass modification remarkably influences the first and second order natural frequency and damp ratio, and has little effect on high order modal frequency and damp ratio. The stiffness modification influences the first five modal frequency and damp ratio remarkably; high order modal frequency and damp ratio are sensitive to stiffness modification. The investigating results reveal the relationship between modal parameter modification and dynamic characteristic of the structure, and lay the foundation for improving overall quality of mechanical products.