In addition to the longitudinal bending and shear deformation of ships in the vertical plane, the effect of longitudinal bending and shear deformation of ships in the horizontal plane coupled with the torsional deformation is particularly considered in the method of theoretical analysis. This theoretical analysis treats the ship as a beam shell with various cross-section in which the actual structure of ship is rather faithfully considered. Concerning the structural idealization, ships are divided into substructures with uniform cross-section and then each substructure is also divided into small strip elements. Further, the experimental works are carried out, using a model of container ship with large hatch openings. And it has been confirmed that the calculated results obtained through this method are in good agreement with the experimental results. The results of this investigations led to the following conclusions. In dealing the longitudinal strength of container ships considering the horizontal bending and torsion, the analytical method described here seems to be effective for the practical use in designing of ships. In the structural analysis of container ships, the cross decks between hatch openings should be treated as a reinforced member arresting the torsional deformation of main hull instead of treating them as a part of it. And it is appropriate to adopt 1.0 as the fixedness of the end connection of cross decks for the practical use in the calculating the torsional strength of the main hull.