In seismic design for a PWR reactor containment vessel (PWR-CV), the reliability assessment about buckling limit state under a seismic loading has been carried out by the method described in JEAG4601 (hereinafter, design by rule). Recently, the static elastoplastic buckling behavior of PWR-CV has also been evaluated by a finite element method (FEM) (hereinafter, design by analysis). The design by analysis can take into account geometrical nonlinearity and changes of the shape of PWR-CV in the FEM model. However, the buckling capacity obtained by this method may depend on the analysis conditions of the material nonlinear characteristics and the shape of the vessel model. We analyzed the buckling behavior of PWR-CV to expand the knowledge on the design by analysis method. The FEM model and input waves were based on the past shaking-table tests by Nuclear Power Engineering Test Center. In order to examine the buckling capacities depending on the analysis conditions, two conditions were applied: (a) conservative ones and (b) realistic ones. The results demonstrated that the buckling capacity highly depended on the analysis conditions above, and the design by rule provided more conservative buckling capacity than the design by analysis.