The　seismic　response　characteristics　of　underground　structures　in　saturated　soils　are　investigated.　A　fully　fluid-solid　coupling　dynamic　model　is　developed　and　implemented　into　ABAQUS　with　a　user-defined　element　to　simulate　the　dynamic　behavior　of　saturated　soils.　The　accuracy　of　the　model　is　validated　using　a　classic　example　in　literature.　The　performance　of　the　model　is　verified　by　its　application　on　simulating　the　seismic　response　characteristics　of　a　subway　station　built　in　saturated　soils.　The　merits　of　the　model　are　demonstrated　by　comparing　the　difference　of　the　seismic　response　of　an　underground　structure　in　saturated　soils　between　using　the　fully　coupling　model　and　a　single-phase　medium　model.　The　study　finds　that　the　fully　coupling　model　developed　herein　can　simulate　the　dynamic　response　characteristics　of　the　underground　structures　in　saturated　soils　with　high　accuracy.　The　seismic　response　of　the　underground　structure　tends　to　be　underestimated　by　using　the　single-phase　medium　model　compared　with　using　the　fully　coupling　model,　which　provides　a　weaker　confining　action　to　the　underground　structure.