Abstract: The rheological parameters of cement-based grout is time-dependent, which has an important influence on building grout diffusion model. Based on the assumption of Bingham fluid and narrow plate model of grouting diffusion, a formula for calculating the diffusion radius in soil is developed considering the time-varying behaviors of grout. It shows that the grouting diffusion radius of Bingham fluid is related to the grouting pressure difference, gap width, flow velocity and time-dependent behaviors of rheological parameters. The law of fracture pressure of grouting is affected by the gap width notably, and the rheological parameters of grout play a key role in computing the diffusion radius. So it is unreasonable to neglect the time-dependent behaviors of grout in computing the diffusion radius. Based on the grouting tests on strong-weathered granite tunnel in Xiamen Airport, the application of the formula of grouting diffusion has proved to be successful in practice. Furthermore, some available results are gained, beneficial to the design and construction of fracture grouting in strong-weathered granite.