Bridge is an important part of transport system, especially for the long-span bridges of important route. And it belongs to the lifeline project. It is an important measure for reducing the secondary disaster to ensure bridge’s normality in traffic after the earthquake. Currently, the isolation seismic design of long-span bridges with the special structure is used to reduce damage of bridges by the reason of the earthquake. Based on damping principle of the viscous dampers, the calculation and analysis of what the effect of shock absorption done by damper in decorate position of long-span cable-stayed bridge to structure of bridges are formulated in this paper.