While　SSI　is　considered,　the　soil　is　often　simplified　by　tow-degree-of-freedom　lumped-parameters　model　which　is　only　suitable　for　isotropic　elastic　soil.　However　the　soil　in　civil　engineering　is　always　layered　and　anisotropic　soil.　In　order　to　simply　the　layered　soil　in　SSI　problem,　the　article　provides　a　new　way　that　is　still　2DOFM　lumped-parameters　model,　but　the　parameter　values　are　identified　the　first-order　polynomial　approximation　method　on　the　basis　of　the　actual　acceleration　records.　The　method　given　in　the　article　have　some　virtues,　such　as　less　computation　and　high　computed　precision,　and　the　results　for　the　model　parameters　are　very　reliable.　The　method　is　operated　in　MATLAB.