To study the influence of viscous damper parameters on the mechanical behavior of long-span railway suspension bridges, a railway suspension bridge with a main span of 1,100 m and asymmetric towers was used as a case study. Using dynamic time-history analysis methods, different damping coefficients and velocity exponents were analyzed for their effects on the dynamic response of the bridge under both train crossing and E2 seismic conditions. The dynamic response results were compared, and a mechanism analysis of the damper's effect on the structural response was conducted. The computational results indicate that, for the train crossing condition, increasing the damping coefficient and decreasing the velocity exponent can reduce the longitudinal displacement at the beam ends while increasing the bending moment at the base of the towers; for the E2 seismic condition, increasing the damping coefficient can reduce the longitudinal displacement at the beam ends and decrease the bending moment at the base of the towers, whereas the value of the velocity exponent has little effect on the structure; the parameters of the dampers should consider various dynamic conditions to ensure control objectives while also considering the energy dissipation capacity and constructability. Finally, parameter design recommendations for nonlinear viscous dampers are proposed.