Abstract: The effectiveness of grouting engineering is determined by the migration and diffusion behavior of slurry within rock fractures, which is a fundamental physical process. Slurry flow resistance, front morphology, and migration-diffusion range are directly influenced by fracture roughness and aperture, which serve as key geometric parameters. A self-developed rock fracture grouting simulation test device was established to reveal the meso-scale regulation of roughness and aperture on slurry migration and diffusion, as well as the associated coupled scour-erosion response mechanisms. A physical model of complex rock fractures is constructed to conduct grouting tests, and the results are inversely validated using PFC^3D numerical simulations. The following findings are obtained: The self-developed device consists of similar material specimen preparation, measurement, and control equipment and a rock fracture grouting simulation test apparatus. Complex rock fracture networks can be reconstructed within a limited three-dimensional space, and grouting tests can be performed, enabling a fully integrated operation from raw material preparation to physical simulation tests. For the sand particles simulating roughness, smaller particle sizes are found to lead to faster slurry migration and diffusion, longer effective migration-diffusion distances, stronger interlocking effects between sand particles, smaller outlet accumulations, and more significant final setting deposition traces of the sand-slurry mixture. The slurry flow area is expanded by increasing the fracture aperture, and long-distance slurry migration and diffusion is driven, while the retarding effect caused by roughness is partially offset. The spatiotemporal evolution characteristics of linear migration and diffusion within the main fracture and discrete or linear heterogeneous migration and diffusion within branch fractures are numerically reproduced by the PFC^3D numerical simulation results. The relative errors between the physical tests and numerical simulations for the maximum migration and diffusion distance in the main fracture are all within 10.0%, verifying the scientific validity and applicability of the self-developed test device in characterizing slurry migration and diffusion behavior. Mechanistic reference for predicting grouting diffusion radii and optimizing process parameters can be provided by the research results.