Soft mattress is the basic structure in waterway regulation project,and the hydraulic characteristics of soft mattress directly affect the protection effect of waterway regulation project.We study hydraulic characteristics of the software mattress ballast block by establishing the normal tank model,such as the flow field structure,the length of the recirculation zone,the velocity of the bottom,turbulent flow field and shear stress.The results show that software mattress ballast block decreases the flow velocity and shear stress near the bottom,and flow velocity in reflux zone,and increases the upper layer velocity and longitudinal turbulence intensity.The software mattress ballast block can adjust the flow pattern near bottom to promote sediment deposition,and improve the beach protecting effect.