When carrying out stress analyses of a Mega-Float structure subject to wave loads, it is in many cases difficult to make an all-in-one program containing both of hydroelastic analysis and stress analysis because of capacity and processing time of computers. To cover such situation, a practical two-step method is proposed in which separately obtained first step output of hydroelastic analysis is given to the second step of stress analysis, where the static analysis program for Mega-Float is used. The stress analysis is done for each of the real part and the imaginary part of the hydroelastic solution to obtain two typical simultaneous set of stresses, and then, calculations of amplitude distributions for experienced maximum stresses while waves pass are done using the two parts. The method is applicable to plane grillage models and also three-dimensional finite element models based on common skeleton consisting of the lines of longitudinal and transverse bulkheads and girders. Hence, flexible application can be done according to various stages of design work. Results of trial analysis are shown for the cases of head sea and diagonal sea applied to the grillage model and the finite element model. From those results, it has been found that the method proposed here can be used as a useful analytical tool for structural design of Mega-Float.