Water inrush and collapse accidents occur frequently due to the unclear diffusion law of the grouts when grouting in water-rich sandy gravel stratum. Grouting model test is an effective method to study the law of grout diffusion. Taking the water-rich sandy gravel stratum in Beijing as the research object, a model test of dynamic water grouting was independently designed. Based on the uniform design method, the spatial distribution and diffusion of cement grout under the influence of gouting pressure, water flow velocity, water-cement ratio and stratum permeability coefficient were studied. The results show that: The grout diffused in an ellipsoid, spherical or columnar shape in water-rich sandy gravel stratum, which is a typical seepage diffusion. Multiple linear regression analysis found that the grouting pressure, stratum permeability coefficient, water flow velocity, water-cement ratio and grout diffusion distance were exponential function relationships. The single factor analysis found that the groundwater hindered the diffusion distance of the grout in the couner-current and vertical water-flow directions. On this basis, some suggestions on the arrangement of grouting holes were put forward.