In this study, to clear the behavior of a Mega-float structure in environmental exciting forces of real sea condition such as wave, current and wind load, we made a pontoon type elastic floating model and carried out model experiments on the characteristics of motions, wave drift force and drag forces in current and wind for a large elastic floating body. And the theoretical results of the wave drift forces for the various water depths and the various bending stiffness are illustrated. When we estimate the behavior and mooring forces of Mega-float structure in real sea condition, we must consider the combined forces acting on the structure and effects of shallow water.