Abstract: Through the summary of seismic strengthening design of Fuchengmen bridges, the design method of Fluid viscous damper (FVD) when seismic strengthening were shown in this paper. By comparing with the conventinal strengthing method, the advantages of using FVD in engineering cost, traffic affects and implementation are discussed herein. The research results show that: for three or four span simply-supported bridges, or continuous girder bridge, the reinforcement scheme of adding viscous dampers, not only is effective, but also has low cost, strong implementation and small traffic impacts, which is suitable for widely application. But when doing seismic strengthing design, displacement goal should be defined clearly and the increase of seismic demanding in the connection members after strengthening should be paid more attention to.