With regard to ship hull girder strength, many papers on measurements in waves and statistical prediction of fluctuating stresses have been already published. The authors have developed a program system of the longitudinal strength of ships including the “Modified beam theory” by Dr. T. Kawai, linked with programs for wave loads calculation by strip method and statistical analysis. In this paper, the comparison of results by the present method and the full scale measurements in still water regarding the torsional strength of container ship with 200m length and the long-term prediction of fluctuating normal stresses on the upper deck have been performed. The main conclusions are as follows ; 1) The results calculated by this system show relatively good agreement with the full scale measurements on the torsional strength of the container ship. 2) The long-term prediction on the container ship in the full loading condition using the Walden's statistical data in the North Atlantic shows the maximum expected fluctuating normal stress on the upper deck with probability level 10^-8 to be 15.9kg/mm² (half amplitude).