Abstract: In order to study the penetration diffusion model for backfill grouting through segments of shield tunnel, taking the exponential fluid as the research object and applying the fluid mechanical theory and capillary group theory, the formulae for calculating the backfill grouting through segments of shield tunnel are deduced, and the application scope and determination methods for the parameters of the formulae are analyzed. Based on a specific case, the influences of the grouting pressure, grout properties (water-cement ratio) and ground conditions (groundwater and permeability coefficient) on the grout diffusion radius and the total pressure on segments are discussed. The result shows that the grouting pressure is linear to the diffusion radius. The diffusion radius increases along with the increase of the grouting pressure, water-cement ratio and permeability coefficient, and decreases along with the increase of the groundwater pressure. The total grouting pressure on segments increases with the increase of the grouting pressure, water-cement ratio and ground permeability, but does not change along with the change of the groundwater pressure.