Simplified　equivalent　static　methods　are　widely　used　in　seismic　design　and　analysis　of　underground　structures.　The　relative　shear　deformation　of　the　soil　is　usually　considered　as　the　main　earthquake　load　in　the　existing　simplified　methods,　including　the　free-field　racking　deformation　method,　flexible　coefficient　method,　response　displacement　method,　response　acceleration　method,　and　pushover　analysis　method.　However,　the　inertia　force　of　the　overburden　soil　caused　by　the　vertical　earthquake　motion　does　not　attract　sufficient　attention　in　many　design　specifications.　The　recent　studies　revealed　that　the　large　vertical　inertia　force　made　a　significant　influence　on　the　shear　strength　and　deformation　capacity　of　the　support　components　in　the　underground　structures,　especially　for　the　shallow　buried　ones.　Firstly,　based　on　the　earthquake　damage　investigation　of　shallow　buried　rectangular　underground　structures　and　the　analysis　model　of　response　displacement　method　(RDM),　this　paper　proposes　the　vertical　inertia　force-response　displacement　method　(VIF-RDM),　in　which　the　vertical　inertia　force　of　overburden　soil　is　taken　into　account.　The　calculation　methods　of　two　critical　parameters　of　the　VIF-RDM　are　described　in　detail,　including　the　coefficients　of　the　foundation　springs　around　the　structure　and　the　maximum　vertical　inertia　force　of　the　overburden　soil.　Afterwards,　the　integral　vertical　inertia　force-response　displacement　method　(IVIF-RDM)　is　put　forward　to　reduce　the　computational　complexity　and　calculation　error　of　the　foundation　springs.　The　surrounding　soil　model　is　directly　used　to　calculate　the　equivalent　earthquake　loads,　which　are　caused　by　the　relative　displacement　of　the　free　field.　The　two　proposed　simplified　methods　and　RDM　are　compared　with　the　time-history　analysis　method　(THAM)　in　a　real　underground　structure.　The　results　show　a　significant　difference　in　the　axial　force　of　the　central　column　between　the　two　proposed　methods　and　RDM.　The　proposed　methods　reflect　the　internal　forces　of　the　structure　under　the　strong　earthquake　more　accurately.　Therefore,　it　can　be　used　to　evaluate　the　seismic　safety　performance　of　the　shallow　buried　rectangular　underground　structures　in　the　future.