The　cross-sea　bridges　play　an　important　role　to　promote　the　development　of　regional　economy.　These　bridges　located　in　earthquake-prone　areas　may　be　subjected　to　severe　earthquakes　during　their　lifetime.　Group　pile　foundations　have　been　widely　used　in　cross-sea　bridges　due　to　their　structural　efficiency,　ease　of　construction,　and　low　cost.　This　paper　investigates　the　seismic　performance　of　bridge　pile　foundation　based　on　the　seismic　fragility　analysis.　Based　on　the　analysis　platform　OpenSees,　the　three-dimensional　finite　model　of　the　bridge　pile　foundation　is　developed,　where　the　pile-water　interaction　is　replaced　by　the　added　mass　method,　nonlinearp-y,t-z,　andq-zelements　are　used　to　simulate　pile-soil　interaction,　and　the　displacement　of　the　surface　ground　motion　due　to　seismic　excitations　is　applied　on　all　spring　supports.　The　seismic　fragility　curves　of　the　bridge　pile　foundation　are　generated　by　using　the　earthquake　records　recommended　by　FEMA　P695　as　input　motions.　The　curvature　ductility　based　fragility　curves　are　obtained　using　seismic　responses　for　different　peak　ground　accelerations.　The　effects　of　pile-water　interaction,　soil　conditions,　and　different　types　of　ground　motions　on　the　bridge　pier　fragilities　are　studied　and　discussed.　Seismic　fragility　of　the　pier-group　pile　system　shows　that　Sec　C　(the　bottom　section　of　the　pier)　is　the　most　vulnerable　section　in　the　example　fluid-structure-soil　interaction　(FSSI)　system　for　all　four　damage　LSs.　The　seismic　responses　of　Sec　E　(a　pile　section　located　at　the　interface　of　the　soil　layer　and　water　layer)　are　much　lower　than　other　sections.　The　parameter　analysis　shows　that　pile-water　interaction　has　slight　influence　(less　than　5%)　on　the　fragility　curves　of　the　bridge　pier.　For　the　bridge　group　pile　foundations　considering　the　fluid-pile-soil　interaction,　PNF　may　induce　larger　seismic　response　than　far-field　(FF)　and　no-pulse　near　field　(NNF).　The　bridge　pile　foundation　in　stiff　soil　is　most　vulnerable　to　seismic　damage　than　soft　condition.