Vertical　seismic　action　has　an　important　effect　on　the　seismic　failure　response　of　underground　structures.　Due　to　the　functional　limitations　of　the　existing　centrifuge　shaking　table　and　the　existing　model　box‚　it　is　difficult　to　directly　simulate　the　site　response　under　multi-directional　seismic　action.　Therefore‚　based　on　a　completed　centrifuge　shaking　table　test　of　underground　structure　with　the　top　of　the　structure　mixed　with　a　certain　proportion　of　steel　sand　to　equivalently　simulate　the　effect　of　vertical　inertia　force　caused　by　vertical　seismic　action‚　and　considering　the　horizontal-vertical　seismic　action‚　a　finite　element　model　of　soil-structure　dynamic　interaction　was　established‚　and　the　correctness　of　the　numerical　model　was　verified.　At　the　same　time‚　the　applicability　of　equivalent　test　method　for　simulating　vertical　inertia　force　induced　by　vertical　ground　motion　of　overburden　steel　sand　was　explored　based　on　the　verified　numerical　model.　The　results　show　that　the　horizontal　seismic　response　of　soil-structure　system　is　not　significantly　affected　by　vertical　seismic　action　and　the　addition　of　steel　sand　to　the　upper　part　of　the　structure.　Compared　with　considering　only　horizontal　seismic　action‚　the　horizontal-vertical　seismic　action　increases　the　peak　response　of　the　total　strain　and　axial　force　of　the　column　and　the　side　wall.　Compared　with　the　horizontal-vertical　seismic　action‚　in　which　the　vertical　and　horizontal　ground　motions　reach　their　peak　at　the　same　time‚　under　horizontal　seismic　action‚　although　the　equivalent　test　method　of　adding　steel　sand　to　the　upper　part　of　the　structure　increases　the　initial　values　of　axial　force　and　total　strain　of　the　central　column　and　side　wall　of　the　structure.　However‚　the　peak　responses　of　total　strain‚　axial　force‚　shear　force‚　bending　moment　and　other　internal　forces　of　the　central　column　and　side　wall　with　steel　sand　are　basically　close　to　those　considering　the　horizontal-vertical　seismic　action.　The　method　of　adding　steel　sand　to　the　upper　part　of　the　structure　can　effectively　reflect　the　total　strain　and　peak　response　of　internal　force　of　the　vertical　load-bearing　member　under　vertical　ground　motion.　Compared　with　the　horizontal-vertical　seismic　action‚　in　which　the　vertical　ground　motion　reaches　its　peak　before　the　horizontal　ground　motion‚　under　horizontal　seismic　action‚　the　equivalent　test　method　of　adding　steel　sand　to　the　upper　part　of　the　structure　may　overestimate　the　peak　response　of　total　strain　of　the　structural　members.　But　it　still　reflects　the　internal　forces　and　total　strain　levels　of　the　vertical　load-bearing　member　at　the　peak　moment　of　vertical　ground　motion.　©　2023　Science　Press.　All　rights　reserved.