The complex topography，water depth and velocity conditions in the construction area of the lower reaches of the Yangtze River are very unfavorable for the formation of the riprap dam.Relying on the section II of the direct waterway regulation project of the 12.5 meters deep waterway below Nanjing of the Yangtze River，the impact of external conditions on the drop point is reduced by modifying the riprap equipment and adding tumbling barrel constraint construction to reduce the riprap height and the riprap drift so as to achieve the purpose of controlling the stone falling point and achieve the precise positioning of underwater riprap.The engineering application effect is good，and the cost is reduced while the construction quality is improved，which provides a reference for the following similar projects.