In the current study, the overall finite element analysis of an ideal Panamax passenger ship is carried out in order to examine the deformation characteristics of luxury cruise ships under the ultimate state and the influence of the initial geometrical imperfection. It is found that the deformation of the superstructure and the main hull at the midship is in the way of double plane section. A method for calculating the ultimate strength of luxury cruise ships is accordingly proposed by using the finite element model between the columns, assuming that the superstructure and the main hull bend and revolve around their respective centroids referring to the "double beam theory". The accuracy of this method is obviously improved by comparing with the conventional finite element method for calculation of ultimate strength.