For an offshore platform structure applied to wave-energy conversion system, in order to catch the maximum waves to generate more powers, similar to wind-energy power generators, a range of angles for the devices normal to the propagating direction of incident waves is required, particularly when the power converting system has directional preference. That is one essential reason why a single mooring offshore platform system is so important in the development of an offshore wave-energy conversion system. The single mooring-system would allow the offshore wave-energy conversion system to turn freely in accordance to the action of strong directions of propagating waves and in this way, most energy induced from the incident waves can be caught and converted into reusable powers. The aims of this study are firstly, based on previous studies to further modify a single moored offshore platform system that may subject to less wave forces in the sea and, secondly, to verify the efficiency of single-moored system by carrying out an experimental testing on a simple single-moored floating platform system in the water tank.