Abstract: In order to explore the diffusion law of viscosity time-denatured slurry in a dynamic water environment, taking NF cement-based slurry as the research object, the time-varying test of slurry viscosity was carried out, and the time-varying function of viscosity was determined. Based on the level set method, by customizing the viscosity time-varying function in the numerical model, the numerical simulation of dynamic water grouting considering the time-varying viscosity of the slurry is realized, and the slurry diffusion pattern and diffusion distance with and without the time-varying viscosity are obtained. The results show that the NF cement-based grouts with a water-cement ratio of 0.6 to 1.0 belong to Bingham fluid, and their viscosity increases exponentially with time. In the process of slurry diffusion, the change of slurry viscosity in the flow field shows two stages: the stable stage and the decline stage. The diffusion shape changes from circular to elliptical at the initial stage to U-shaped at the end; the slurry diffusion distance is positively correlated with time, and decreases with the decrease of water-cement ratio; the diffusion distance obtained without considering the slurry viscosity is always greater than that obtained with considering the slurry viscosity, and with the increase of grouting time, the effect of the time-varying properties of slurry viscosity on the diffusion distance is more significant.