A series of buckling eigen-value calculations and elastoplastic large deflection analyses of simply upported continuous plate with cutout under thrust has been performed. Firstly, simple formulae for estimation of elastic buckling strength have been derived based on the results of eigen-value calculations. Secondary, it has been clarified that the buckling strength evaluated by the existing plastic correction methods exceeds the ultimate strength in some combinations of plate thickness and cutout diameter. So, new plastic correction formula considering the yielding effect for estimation of buckling strength of continuous plate with cutout has been proposed. Finally, by focusing on the characteristics of ultimate strength obtained by elastoplastic large deflection analyses, simple formulae for estimation of ultimate strength of continuous plate with cutout have been derived.