The objectives of present. paper are to develop the estimation method for the hydrodynamic forces on very large floating structures in the vicinity of a breakwater and to clarify the characteristics of elastic response on the very large floating structures (VLFS). In the present paper. the source distribution method was applied to prediction of by hydrodynamic forces on VLFS and the elastic responses of VLFS were computed by model analysis. From the results of numerical calculation, the effects of breakwater on the elastic response of VLFS and the characteristics of elastic responses on the phase two model of VLFS were made clear.