Abstract: With the increase in the depth of coal resource mining and the extension of underground engineering to deeper areas, the problem of sandstone pore water damage has become increasingly prominent. Chemical grouting is an effective method for the treatment of water damage in deep pore rock layers. However, it still faces technical bottlenecks such as low filling rate and poor seepage reduction effect. In order to study the laws of filling, seepage, diffusion and reducing seepage of chemical grout in pores, the near-transparent quartz sands and neutral silicone adhesives were used to prepare the porous medium model material, and the self-constructed plexiglass tube was used to prepare the experimental model, and stained urea-formaldehyde resin grout as the grouting liquid. We realized visual observation of grout seepage diffusion process, measured the porosity, seepage, seepage reduction rate and filling rate of the porous medium, and further investigated the effects of chemical grout on the filling characteristics and seepage reduction mechanism of the porous medium. The results showed that when the grout flows through the saturated cemented porous medium, there is no obvious interface between the seepage range and the non seepage range, and the grout pore-filling rate tended to decrease with increase of the distance from the grouting entrance; the seepage law of chemical grout in saturated porous media is between the piston and non-piston type displacement modes; within the range of grout diffusion, the seepage of the model material is significantly reduced, with the measured water reduction rate exceeding 97%. As the distance from the grouting inlet increases, the water reduction rate shows a decreasing trend.