Water-pile-soil　interaction　and　the　three-dimensional　scattered　wave　effect　play　crucial　roles　in　the　seismic　response　of　structures　built　on　saturated　seabed　subjected　to　vertical　P-wave　incidents.　This　study　proposes　a　fully　coupled　three-dimensional　continuum　model　of　water-pile-saturated　media　to　investigate　the　seismic　response　of　the　system　under　vertical　seismic　excitation.　By　employing　Helmholtz　decomposition　and　the　method　of　variable　separation,　the　governing　equations　are　decoupled　based　on　assumed　boundary　and　interface　conditions,　yielding　the　solution　equation　in　the　frequency　domain.　The　effects　of　various　pile　and　soil　parameters　on　the　seismic　response　are　analyzed　from　multiple　perspectives,　along　with　the　impact　on　the　spatial　distribution　of　three-dimensional　scattered　wave　effects.　Results　indicate　that　the　seismic　response　of　piles　and　saturated　soil　is　significantly　influenced　by　the　presence　of　water　and　the　three-dimensional　scattered　wave　effect.