Abstract: A two-dimensional elastic foundation model to analyze the buckling of elliptical face-core ddaminations in composite sandwich plates is established.A displacement function is found to properly describe the buckling shapes of ddaminations.The buckling loads and effcctivc boundary fixity coefficient C' of ddaminations are obtained by Raylcigh Ritz energy method.It is found thatthc film dclamination model can not reflect the effect of the core on delaminations by transverse elastic support,and can only give the upper critical buckling load of dclaminations.Also the relations between the parameters of the ddamination and the effctive boundary fixity coefficient C' arc analyzed.