Water　tank　is　one　of　the　most　important　components　of　passive　containment　cooling　system　(PCS)　in　advanced　nuclear　power　plant.　Moreover,　the　dynamic　characteristics　of　shield　building　and　auxiliary　building　might　be　changed　because　of　fluid-structure　interaction　(FSI)　of　the　PCS.　Therefore,　FSI　between　cooling　water　and　the　shield　building　should　be　considered　in　the　dynamic　analysis　of　the　nuclear　island　building.　To　study　the　FSI　effect　and　propose　an　effective　and　simplified　method,　three　numerical　models　were　established　and　analyzed　under　three-dimensional　seismic　loadings.　Acceleration　time　histories　of　reference　points　in　the　shield　building　and　auxiliary　building　were　got　and　floor　response　spectra　were　calculated.　The　results　show　that　FSI　effect　could　not　be　regarded　to　decrease　the　seismic　response　simply　but　it　should　be　considered　in　structure　design　and　analysis.　A　simplified　model　is　proposed　in　this　study　and　proved　to　have　a　good　agreement　with　the　FSI　model　in　the　curves　of　floor　response　spectra.　The　conclusions　could　provide　reference　for　further　study　in　the　field　of　nuclear　island　building.　(C)　2017　Published　by　Elsevier　Ltd.