Most　subway　stations　in　China　have　been　constructed　recently　and　their　seismic　performance　and　potential　failure　modes　are　not　well　characterized.　This　paper　is　dedicated　to　identifying　potential　failure　modes　of　underground　frame　structures　through　numerical　simulations,　and　developing　an　optimized　method　for　upgrading　the　seismic　performance　of　deficient　structures　via　controlling　the　potential　failure　modes.　The　dynamic　response　of　an　unequal-span　subway　station　structure　was　calculated　considering　different　ground　motions　with　increasing　peak　horizontal　acceleration,　and　the　structural　seismic　performance　characteristics　were　evaluated.　Seismic　performance　evaluation　indexes,　including　interlaminar　deformation　risk　factor　of　columns　and　sidewalls　and　deflection　risk　factor　of　slabs,　were　established　to　identify　the　most　critical　structural　component　under　strong　earthquake　excitations.　The　structure　failure　mechanism　was　analyzed,　and　consequently,　the　corresponding　retrofitting　scheme　for　upgrading　its　seismic　performance　was　proposed.　Finally,　the　structural　responses　before　and　after　retrofit　were　calculated　and　compared　to　demonstrate　the　effectiveness　of　the　retrofitting　scheme.　The　results　can　improve　the　understanding　of　the　failure　modes　of　underground　frame　structures　and　provide　references　for　their　seismic　design.