Supporting structures for the large offshore wind turbine generator such as five mega watt preferably do not receive large wind force, since the bottom diameter of a conventional cylindrical shell tower becomes as large as seven meters. Further, they may have proper rigidity, because the first natural period of the structure stays away from a rotating period of a rotor and wave periods. Thus, we have proposed a supporting structure of a truss tower and a jacket because of their structural continuity to examine weights, stiffness and natural periods, comparing those of a cylindrical tower and a monopile. Then, we conducted inelastic analysis of the proposed structure taking soil and pile interaction into consideration to know the effect of soil foundation. Moreover, we carried out the push over analysis to evaluate the ductility of it. The paper describes the comparison of these kinds of properties for both structures.