Combining with the design bidding Phase 1 of Yangtze River downsteam from Nanjing 12.5 m Deep-water Navigation Project,we propose a new structure of triangular caisson and its design method.The study on the new structure indicates that such a triangular caisson can significantly enhance the stability against overturning and sliding and also reduce the foundation pressure if the angle between the side plate and horizontal plane is no more than 60 degrees.Such a structure has not only the advantages of mound breakwater,such as no standing wave effect,little wave pressure,foundation pressure and less restrictive requirements for the ground bearing capacity,but also those of gravity structures,namely the usage of fewer rocks and high efficiency of installing prefabricated components.To sum up,the new structure of triangular caisson can be applied to breakwater,sand-control dam and regulating structures,etc.