Authors have developed the offshore structure for control of sea environment named S-VHS construction method, which is composed of the sloping top slit-type caisson and steel pipe piles. The sloping top form enables to realize the remarkable reduction of wave force exerted on the dike body compared with the conventional one. 11111In this paper, hydraulic feature with wave dissipation ability and wave force reduction effect are verified through some hydraulic experiments. After the preliminary study for the valid structure form, reflection and transmission ability for the selected structure models were tested with the hydraulic experiment relevant to the ratio of caisson width and wave length. Finally, wave force experiment was executed and it revealed the performance of wave force reduction. Based on the results, we proposed specific design wave force formula for S-VHS construction method.