Seismic　failure　mechanism　of　underground　frame　structures　presents　that　the　collapse　of　underground　structures　attributes　to　the　insufficient　seismic　resistance　of　central　columns.　Therefore,　researches　have　been　conducted　to　improve　the　seismic　performance　of　underground　structures　by　enhancing　the　loading-carrying　capacity　of　the　central　columns　or　decreasing　the　seismic　loads　transmitted　to　central　columns.　For　this　purpose,　this　study　proposed　a　new　approach　by　changing　the　connection　type　between　sidewalls　and　slab:　setting　shock　absorbing　gap　(SAG)　between　sidewalls　and　ceiling　slab,　which　aims　to　decrease　seismic　loads　transmitted　to　central　columns.　The　proposal　and　working　mechanism　of　SAG　were　illustrated　detailedly.　Afterwards,　nonlinear　finite　element　models,　in　which　a　developed　elastoplastic　constitutive　model　was　used　to　simulate　the　3D　strength　and　softening　behaviour　of　surrounding　soils,　were　built　for　simulating　the　static　and　dynamic　responses　of　underground　structures.　Based　on　the　numerical　results,　SAG　affecting　the　internal　forces　of　structural　components　before　earthquakes　were　discussed　firstly.　Then　the　seismic　efficiency　of　SAG　updating　the　seismic　performance　of　underground　frame　structures　was　analyzed　by　discussing　earthquake-induced　damage　mode　of　overall　structures,　soil　pressure　on　structures,　earthquake-induced　deformations　and　internal　forces　of　structural　components.　Finally,　the　seismic　performance　of　underground　frame　structures　influenced　by　the　width　of　SAG　and　frictional　coefficient　of　the　sliding　surface　was　investigated,　and　advice　for　reasonably　using　SAG　was　suggested.