A　high-order　time-domain　boundary　element　method　(TDBEM)　for　evaluating　the　combined　impact　of　earthquakes　and　waves　on　sea-crossing　bridge　piers　is　presented,　facilitating　a　comprehensive　simulation　of　the　interactions　among　seismic　activity,　wave　forces,　and　structural　responses.　The　proposed　method　is　validated　through　numerical　simulations　from　existing　studies　and　benchmark　model　tests.　An　elliptical　pier　is　used　as　a　case　study　to　analyze　these　combined　effects.　Results　indicate　that　water　depth　significantly　influences　structural　seismic　responses　due　to　changes　in　fundamental　frequencies　caused　by　added　water　mass.　The　influence　of　waves　in　the　combined　action　is　contingent　upon　the　dominant　seismic　frequencies　and　the　structural　fundamental　frequencies.　When　the　structural　fundamental　frequency　is　far　from　typical　ocean　wave　frequencies,　fluid-structure　interaction　(FSI)　effects　amplify　the　peak　response　by　8　%　to　25　%,　depending　on　the　ground　motion＇s　dominant　frequency.　When　the　structural　fundamental　frequency　coincides　with　typical　ocean　wave　frequency　ranges,　FSI　effects　exhibit　an　uneven　influence　on　the　structural　response　due　to　the　inhomogeneity　of　wave-induced　FSI　effects.　In　such　conditions,　as　the　dominant　frequency　of　ground　motions　increases,　the　suppression　effect　induced　by　wave　FSI　on　the　peak　response　may　counterbalance　or　exceed　the　influence　of　earthquake-induced　FSI　effects.