In order to reveal the influence law of viscous dampers on the seismic reduction effect of long-span cable-stayed bridges, parameter analysis and optimization design of viscous dampers are carried out. Taking a certain cable-stayed bridge project as the engineering background, a spatial dynamic model is established. Based on the nonlinear dynamic time history analysis method, the dynamic response of the long-span cable-stayed bridge with dampers is calculated and analyzed. The results show that by selecting appropriate damper parameters and placement positions, the longitudinal displacement of the main beam and tower top of the structure can be effectively reduced, while improving the stress on the pier bottom and solving the seismic problem of long-span cable-stayed bridges; Taking into account factors such as the production and installation of dampers, a damping coefficient of 6000kN?s/m and a velocity index of 0.4 can achieve good seismic reduction effect for the bridge; Based on the seismic response analysis results of the structure under different damper layout schemes, the optimal damper layout scheme for the bridge is proposed.