Damping coefficient and damping exponent play a dominant role on the displacement constraint effect and the damping force of the fluid viscous damper. In this paper, parametric sensitivity study of the fluid viscous damper is carried out by using nonlinear dynamic time history method based on a long suspension bridge. Acceptable damping force and reasonable displacement between stiffening girder and tower are set as the optimization objectives of the damping parameters. It is shown that: as to long suspension bridge, bigger damping coefficient can lower the displacement but increase the force of the dampers, and the smaller damping exponent can aggravate the trend. Fluid viscous damper can play the biggest role of displacement constraint effect while with little additional seismic force is introduced in the whole structure with suitable damping parameters.