Abstract: Based on the proposed mechanical hypothesis and the analytical model of the grid stiffened composite panels, a new smeared stiffened theory was derived for analysing the global stability of grid-stiffened panels. The theory fully considered the effects of shell-stiffener interaction and influence of mid-plane shift. In this theory, the method is applicable for different types of grid stiffened elements. A general eigen function was deduced for computing global buckling load combined with a Rayleigh-Ritz method. The testing sample results were compared with those from the existing smeared stiffener theory, and they exhibited in good agreement. This proves the effectiveness of the proposed method.