A　simplified　analytical　model　is　developed　for　the　couple　vibration　of　an　interaction　system　including　saturated　soils,　pile　group,　and　superstructure　under　vertical　time-harmonic　motion　of　bedrock,　based　on　Boer＇s　poroelastic　theory.　The　corresponding　analytical　solutions　for　the　dynamic　impedance　and　amplification　factors　are　further　obtained　by　employing　potential　function　and　separation　technique　of　variables　which　are　verified　by　comparing　with　existing　solutions.　In　the　analytical　model,　the　soil　is　considered　as　a　fluid-filled　poroelastic　medium,　while　the　pile　and　the　superstructure　are　simplified　as　Rayleigh-Love　rods.　In　addition,　a　parametric　study　is　performed　to　investigate　the　effects　of　pile-soil　parameters　on　the　dynamic　amplification　factors　of　the　interaction　system.