The　saturated　soil　exits　widely　on　the　earth.　The　soil　should　be　considered　as　two　phase　medium　of　solid　and　fluid.　The　equivalent　viscous-elastic　artificial　boundary　element　is　studied　regarding　the　effects　of　energy　radiations　of　solid-fluid　medium　based　on　the　u-p　type　of　Biot　equation　of　saturated　soil.　The　wave　input　is　realized　by　the　equivalent　load　of　earthquake　on　the　node　of　artificial　boundary.　Its　calculation　precision　is　verified　by　comparison　the　examples.　A　nonlinear　finite　dynamic　model　of　saturated　soil-subway　station　is　proposed　for　analyzing　the　wave　propagation　of　soil　in　two　phase　medium　and　comparing　with　the　seismic　response　in　saturated　soil　and　single　phase　soil　under　earthquake.　The　numerical　results　are　compared　with　the　results　obtained　from　shaking　table　test.　The　results　are　shown　that　it　is　more　reasonable　to　use　the　characteristics　of　multi-pore　medium　to　analyze　foundation　soil　under　earthquake　motion　than　to　use　the　single　phased　medium.　The　seismic　response　of　saturated　soil　and　underground　structural　interaction　system　is　studied　through　analyzing　the　acceleration,　displacements　and　internal　forces　of　the　key　elements　in　the　station.　©　2015,　Academia　Sinica.　All　right　reserved.