It is well known that J.Gray demonstrated on the basis of engineering calculations in 1936 that it is possible for dolphins to attain their high swimming speeds only in the case of total laminar flow. Swimming locomotion under conditions of turbulent flow, would require approximately seven times the power which are estimated to be capable of producing. As is known, hydrodynamic thrust in dolphin locomotion, chiefly, is generated by periodically repeating oscillatory motions on the vertical plane of tail fin of complex shape. At the present time we possess incomplete data for shape of a tail fin. Therefore, at the present stage of investigation with the aim of finding the thrust of a tail fin, it is important to obtain shape and steady state characteristics of a tail fin. In order to investigate into the steady state characteristics of a tail fin, the three component tests has been attempted for a half sized tail fin model in towing tank, and the results is compared with the calculated values of the wing theory.