Abstract: By examining the cabin structure with large opening， the longitudinal axial stress distribution under displacement load on the first deck is investigated with three different computational models， using the Finite Element Method（FEM）. Numerical results show that the axial stress distribution displays a heterogeneity of large degree， and such distribution could be obtained with acceptable accuracy via either the double grillage structure model or the cabin structure model. Also， the advantages and disadvantages of two methodologies that can be applied on the longitudinal design of the first deck with large opening are analyzed based on their stability. In order to improve the material utilization and balance the stability requirement for different regions of longitudinal， the non-uniformity of deck longitudinal axial stress distribution is advised to be considered for the design of deck longitudinal.