This study is to simulate a detached breakwater that offers not only a good shelter region for aquaculture cages in its lee but also cost effective. At the first step, a relatively simple 2-D boundary element method had been adopted to simulate the waves passing around various upright detached breakwaters. Based on the results of shelter effect, an opening with angle shape upright breakwater was determined and chosen for further study. Then a 3-D boundary element method is applied to simulate the shelter effect for various heights of breakwater in z-direction in order to achieve the optimal effect. According to the floating breakwater model, it shows that the average diffraction coefficient in the cage region is 0.387 with smaller material volume 9000 m3, which is far bellow 27000 m3 for the upright breakwater. Therefore, it suggests that floating breakwaters with angle should be used in cage aquaculture if the shelter region is required.