In the reclamation and land reclamation project,underwater sanding is required to be completed by blow-filling.In the past,construction techniques used during underwater sanding were likely to cause water pollution.At the same time,sand concentration and sand particle size distribution in the sand fill area were very uneven.This paper introduces an environment-friendly underwater closed diffusion sanding device,which is designed according to the principle of hydrodynamics,adopts a closed diffusion-type structure with internal baffles to achieve large-area,high-efficiency,as well as environment-friendly sanding operations.The underwater closed diffusion type hydraulic sanding device consists of an inlet section,a diffusion section and an inner baffle plate.The computational fluid dynamics(CFD)method is used to simulate the internal flow of the sanding device with clear water as the medium,and the influence of different baffle plates on the flow characteristics and sanding uniformity of the sanding device is analyzed.The final designed underwater sanding device has the advantages of environment-friendliness during construction,simple structure,large single-sand sanding area,high sand-laying efficiency,uniform sand distribution,etc.