Abstract: he shear deformation character in the interface between soil and structural material is str-died.The hyperdolic relationship between shear stress and relative shear displacement is denied.The rigid-plastic deformation relationship is suggested.Anew kind of interface element with thickness is de-veloped.It can dovetail with nonlinear elastic or elasto-plastic models of soils,and can reflect the de-formation in the interface and its nearby shear failure area reasonably.Metod of determining the thick-ness of interface element is proposed.