Abstract: Based on the existing classical model of sandwich panels and energy principle, the equilibrium differential equations of square-honeycomb sandwich plates subjected to in-plane loads are derived, considering the geometry characteristics of the face sheets and the core. The critical pressure of global buckling for simply supported square-honeycomb sandwich plates subjected to in-plane uniform pressure is obtained by using Fourier series and weighted residual method. And the result is compared with that of the finite element analysis to validate the proposed method. Furthermore, effects of geometrical parameters including cell size, core height and face sheet thickness on the global buckling are discussed in the analysis. Numerical results show that core height and face sheet thickness have more effect than cell size on the global buckling of square-honeycomb sandwich plates.