Mud inrush disaster is a typical geological disaster during the construction of mountain tunnels, which may bring immense economic losses and is very harmful to the local environment. Permeation grouting is an important treatment method for mud inrush disaster, which has been wildly used in China. In this paper, a theoretical model of permeation diffusion of Bingham fluid considering gravity is presented. A set of visual permeation grouting experiment device was designed. The test results verify the new permeation diffusion model showing that the slurry is spherical diffusion, while the strip-shaped diffusion appears under the spherical diffusion. With the increase of grouting quantity, the spherical diffusion radius increases gradually. Meanwhile, both the number and radius of the stripshaped diffusion increases gradually. The regression analysis of grouting quantity of 30 typical test data shows that the degree of influence of the grouting quantity from big to small is: grouting pressure, permeability coefficient, and water-cement ratio. The statistics of the total grouting quantity and the grouting quantity of spherical diffusion indicate that the grouting quantity of strip-shaped diffusion accounted for about 50%, which shows the importance of strip-shaped diffusion in surrounding rock reinforcement. This new diffusion model has certain guiding significance for practice.