The purpose of this study is not only to investigate the impacts of mooring line failure for box-shape aquaculture net cages but also to propose an improved solution to prevent this event occurred. In this study, three different scenarios including central mooring line failure, lateral mooring failure, both central and lateral mooring line failure are adopted. The most serious condition is found in the case of both central and lateral mooring line failure. The ratio of maximum mooring tension between the most serious condition and the normal condition is about 1.48. This value can use to determine the safety factor of mooring system. The improved solution is deploying three additional mooring anchors on the upstream side, the results show that this solution can significantly reduce the maximum mooring tension on each upstream anchors compared to the normal condition.