In order to more intuitively observe the process of grouting diffusion and mud film formation in the shield mud film formation test, this paper developed a set of visual grouting test system for the excavation surface of the mud-water shield. The visualization test of the mud infiltration process of the mud-water shield under variable conditions, recording the infiltration images of each transverse and longitudinal section, and binarizing the images, exploring the influence of formation particle size and slurry viscosity on the mud diffusion pattern, and evaluating the formed mud The research results show that the permeability of the slurry in the formation is an important criterion for evaluating the quality of mud film formation, and the pore size of the formation and the viscosity of the mud are important factors affecting the penetration distance of the slurry. Under the condition of high permeability soil layer, reducing the opening ratio of the shield machine cutter head and reducing the grouting pressure can help to form a mud-skin type mud film. The test results have important guiding significance for the mud engineering of shield tunneling.