To investigate the influence of the particle size composition of coarse particles in bentonite slurry on the slurry penetration behavior, this paper built a particle flow numerical model based on dynamics and element modeling. By forming pores with spherical particles and using the actual particle size distribution in the slurry as the reference, the fine particles and sand particles with a diameter exceeding 20 μm in the actual slurry are simulated. Based on the previous penetration tests, corresponding numerical calculations are carried out. The simulation results show that: (1) The composition of different coarse particle diameters in the slurry has a significant impact on the process of penetration and clogging. As the diameter of the coarse particles in the slurry gradually increases, the mass of slurry particles consumed shows a trend of first decreasing and then increasing. This confirms the conclusion that for a specific pore medium, there exists an optimal diameter of coarse particles. (2) Adding an appropriate amount of continuous gradation coarse particles with diameters smaller than the optimal size to the slurry results in the minimum slurry consumption during the penetration. The simulation results are consistent with the research conclusions of the laboratory tests. (3) On each particle penetration path, the aperture is random, and the stagnation depth of the particles is different. For particles with same diameter, the penetration depth has a certain regularity. The smaller the particle, the wider the range of its distribution. (4) In practical, it is recommended to use 0.2D₁₅ (particle size for which 15% by weight of particles in strata) as the optimal clogging particle size. Alternatively, this size can be determined through permeability tests. By uniformly adding sand particles smaller than the optimal clogging particle size to the bentonite-based slurry, a slurry with a lower permeability and fluid loss under the same conditions can be prepared.