Seismic　performance　of　rectangular　underground　structures　as　a　hot　topic　was　studied　systematically　for　decades.　However,　less　attention　was　paid　to　the　functionalities　of　the　structural　components.　This　paper　presents　a　detailed　numerical　investigation　of　the　seismic　responses　of　rectangular　underground　structures　and　aims　to　explore　the　functionalities　of　the　structural　components.　A　three-dimensional　numerical　model　for　nonlinear　dynamic　responses　simulations　of　underground　structures　was　built,　and　the　seismic　responses　of　a　rectangular　underground　structure　under　multiple　ground　motions　were　simulated.　Dynamic　response　data,　including　internal　forces,　drifts　of　the　columns　and　walls　were　obtained　and　analysed.　Results　of　the　proportions　of　seismic　loads　undertaken　by　the　structural　components　explicitly　illustrated　the　functionalities　of　the　structural　components　before　and　during　earthquakes.　Then　the　failure　process　of　Daikai　station　during　the　Great　Hanshin　earthquake　was　simulated,　and　the　loading　and　deformation　capacities　of　the　slabs,　as　well　as　the　intermediate　columns　and　lateral　walls,　were　presented.　In　terms　of　the　load　carrying　capacities　and　functionalities　of　the　structural　components,　the　failure　mechanism　of　the　structures　was　better　to　understand,　and　the　intermediate　columns　as　the　supporting　components　for　the　rectangular　underground　structures　were　proposed.　The　conclusions　are　beneficial　to　the　seismic　design　of　underground　structures.