Based on an actual longspan continuous bridge, the seismic mitigation mechanism and effect of Lockup device, fluid viscous damper and double spherical seismic bearing were investigated and the applicable condition of these seismic mitigation devices are disscussed. The results show that lockup devices do not dissipate seismic energy and can reasonably distribute the seismic inertial force of girder, but may increase the total inertial forces of girder. Fluid viscous dampers, which do not change the structural dynamic characteristics such as structural period and vibration shape, mainly dissipate the seismic energy and reduce structural dynamic response by damping force. Double spherical seismic bearings provide flexibility to lengthen the natural period of the bridge and increase the energy dissipation capacity. However, compared with the response of corresponding nonisolated bridges, the relative displacements between girder and pier increase while decreasing seismic forces of the fixed pier.