Abstract: The paper deals with the laminated composites consisted of two different isotropic materials.With the displacements and their derivatives and stress vectors at the interfaces,the displacement in a layer is expanded.For such expansion the continuity conditions of displacement and stress at interfaces are satisfied automatically.By applying a variational theorem without constraint,Eider equations at interfaces are derived,from which the field equations of a higher order continuum model are obtained.Two extreme cases long wave and short wave approximations are considered.The calculated results for dispersion curve including the past band and stop band show a good agreement with the existing theory.