A spatial finite element model was established to study the influence of viscous dampers on the shock absorption of long-span cable-stayed bridges. The nonlinear dynamic time-history analysis method was employed to calculate the dynamic response after the installation of dampers, and a parametric analysis and optimized design were carried out on viscous dampers. By selecting appropriate damper parameters and layout positions, the longitudinal displacement of the main tower and girder was effectively reduced, while the force at the pier bottom was improved, and the seismic problem of cable-stayed bridges was solved. Considering factors such as the production and installation of dampers, when the damping coefficient of the bridge was 6000 kN·s·m−1 and the velocity index was 0.4, better seismic reduction effects are achieved. After analyzing different damper layout schemes, the optimal scheme of damper layout for the bridge was proposed.