The　hydrodynamic　pressure　expression　based　on　radiation　theory　is　very　complicated　and　temporal　convolution　in　the　time　domain　that　lead　to　their　values　difficult　to　be　calculated.　The　Morison　equation　is　a　semi-empirical　formula　and　its　inertia　coefficient　and　drag　coefficient　are　difficult　to　be　determined　accurately.　Therefore,　the　simplified　formula　based　on　radiation　theory　which　is　concise,　accurate　and　global　decoupling　in　the　time　domain　is　presented　by　introducing　three　dimensionless　parameters　including　frequency　ratio,　wide　depth　ratio　and　relative　height　of　bridge　pier.　By　analyzing　the　analytical　formula　of　hydrodynamic　pressure　detailed,　the　hydrodynamic　pressure　formula　in　the　frequency　domain　is　simplified　by　segmenting.　The　simplified　formula　which　is　global　decoupling　in　the　time　domain　can　be　expressed　in　the　form　of　added　mass　in　low　frequency　vibration　and　can　be　expressed　in　the　form　of　added　mass　and　added　damping　in　high　frequency　vibration.　The　calculation　results　show　that　the　simplified　method　is　in　good　agreement　with　the　analytical　formula.　Compared　with　the　Morison　equation　whose　coefficients　need　to　be　selected　by　experience,　the　coefficients　of　the　simplified　formula　are　only　related　to　the　relative　size　of　bridge　piers.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.