In　this　study,　a　transient　seismic　structure-water-sediment-rock　(SWSR)　interaction　model　is　proposed　to　evaluate　seismic　response　of　marine　structure　in　ocean　space　under　obliquely　incident　earthquake,　in　which　the　dynamic　interaction　between　structure　and　its　surrounding　media,　and　wave　radiation　effect　of　truncated　semi-infinite　far　field　domain　are　fully　considered.　One　particular　advantage　of　the　model　is　that　the　sediment　layer　in　ocean　space　is　more　realistically　modelled　as　fluid-saturated　poroelastic　medium.　Three　main　procedures　are　included　in　establishing　the　model:　first,　a　finite　element　equation　of　near　field　domain　is　established　to　model　multimedia　interaction;　then　a　viscous-spring　absorbing　boundary　condition　is　used　to　simulate　wave　radiation　effect　of　truncated　far　field　domain;　and　in　the　last,　equivalent　earthquake　loading　is　obtained　from　seismic　free　field　response.　The　model　can　be　solved　by　a　standard　time　integration　algorithm　such　as　implicit　Newmark＇s　method.　The　validity　of　the　numerical　framework　to　establish　the　SWSR　interaction　model　is　demonstrated　by　analyzing　three　degenerated　models　and　comparing　with　reference　solutions.　The　seismic　SWSR　interaction　model　is　finally　applied　to　assess　seismic　response　of　an　immersed　tunnel,　with　emphasis　on　the　effects　of　sediment　properties　here　including　thickness,　porosity　and　permeability,　and　the　seismic　wave　incident　angle　on　structural　dynamic　responses.