Redevelopment of the domestic small fishing ports is being started in earnest by applying the environmentally friendly technology in order to attract tourists. For the purpose of improving water quality in the harbor, selection of breakwater type might have the priority to secure calmness and stability and to enhance circulation to the coastal and harbor areas. Therefore, from this study, the hydraulic characteristics of reflective and transmission rates with the installation efficiency and stability of the cylindrical slit type of blocks were analyzed through the hydraulic model experiment. These results were introduced to the numerical analysis for the prediction of wave transformation and water circulation in and out of the structure planned. Two small fishing ports in southern Korea, are affected by the waves of SE through SSW directions and weak tidal currents. The results from the slit type block breakwater compared with those from the rubble mound and curtain wall breakwaters to show the effectiveness of harbor calmness and water circulation. Considering that weak tidal current at the selected areas, the pass rate of a long period wave seems to be still excellent. It was found through this study that the primary objective of wave control and the secondary objective of improving water exchange by the cylindrical slit type coastal structure are satisfied simultaneously.