In general, a deck plate of a ship hull is subjected to mainly in-plane tensile and/or compressive load due to longitudinal bending moment acting the ship. When the strength of a deck plate is considered, the contribution of the plate elements (panels) subdivided by stiffeners and girders are very important, and the accurate evaluation of their compressive ultimate strength is essential. In this report, based on the results obtained in this series of research, the authors have developed a simple prediction method of the ultimate strength with a limited amount of information on the kind of steel, sizes of deck plate panel, welding condition, etc., which does not require complex calculation such as FEM. The main results obtained in this study are as follows. (1) In order to estimate the influence of actual complex initial deflection, the effective coefficient of initial deflection is rationally determined for the standard initial deflection which is idealized from the actually measured initial deflections. The coefficient indicates that the maximum initial deflection influences the ultimate strength fully for thick plates and less than a half for thin plates. (2) The ultimate strength of a deck plate panel with initial imperfections (deflection and residual stress) can be evaluated from the ultimate strength formulae proposed in the previous report, taking into account of the above effective coefficient of initial deflection. The predicted ones are very accurate in the comparison with those obtained by direct FEM calculation to the actual panels.