In　order　to　analyze　the　effect　of　chloride　ion　corrosion　on　seismic　performance　of　offshore　bridge　structures,　a　time-varying　seismic　fragility　analysis　method　for　offshore　bridges　was　proposed.　An　offshore　bridge　of　simply　supported　beam　was　taken　as　an　example,　the　degradation　law　of　longitudinal　reinforcement　diameter　and　yield　strength,　stirrups　diameter　and　cover　concrete　compressive　strength　were　obtained　based　on　the　probabilistic　method,　and　the　results　show　that　the　pier　with　small　shear-span　ratio　changes　from　flexural　failure　to　flexural　shear　or　shear　failure　with　the　steel　corrosion　degree　increasement.　The　finite　element　model　of　piers　considering　bending,　bond-slip　and　shear　deformation　at　different　service　time　were　established　by　OpenSees　software,　and　pushover　analysis　and　incremental　dynamic　analysis　were　carried　out　to　evaluate　the　seismic　performance　of　corroded　pier.　The　damage　states　of　corroded　pier　were　defined　and　the　damage　states　capacity　was　evaluated,　then　the　time-varying　seismic　fragility　curves　of　the　bridge　were　obtained　by　the　fragility　analysis　method.　The　results　show　that　under　the　influence　of　chloride　ion　erosion,　the　material　performance　of　the　pier　is　degraded　continuously,　and　the　seismic　fragility　of　the　offshore　bridge　increases　with　its　service　time.　©　2019,　The　Editorial　Board　of　Journal　of　Basic　Science　and　Engineering.　All　right　reserved.