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.
 In 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.