Abstract: The large deflection dynamic plastic response of built-in square plates with one-way stiffener under blast loading was analyzed based on the motion equations of both panels and stiffeners.The analy-sis indicats that there are three motion models for the stiffened plate,depending on the relative rigidity of the stiffener and the peak load applied.The paper is confined to discussion of the global deflection model and presents the me mbrane solution by neglecting the influence of bending moment.The calculation re-sults were compared and found to be in good agreement in most cases with the existing experimental re-sults.It shows that the current sim plified analytical method can be used to predict the permanent defor-mation of one-way stiffened square plates under blast loading in a more rational manner.