Ordinary cement slurry suffers from drawbacks such as rapid settling, low filling efficiency in micro-fractures, and poor injectability. To meet the requirements of grouting engineering applications, modification of the performance of ordinary cement slurry holds significant research value. This study aims to enhance the suspension properties, stone formation rate, and impermeability of the slurry by modifying it with sodium-based bentonite. Through basic performance testing and microscopic structural observation of the slurry, the study ultimately determined the optimal addition range of bentonite. Injection tests were conducted using a transparent pore channel model and a 3D-printed transparent rough single-crack model to validate the superiority of the modified slurry. The research results show that: adding approximately 3 % sodium-based bentonite to ordinary cement slurry significantly improves the slurry’s suspension properties, reduces water separation rates, and increases stone formation rates; in grouting experiments conducted using a transparent pore channel model, the optimal modified slurry (water-cement ratio of 1, bentonite content of 3 %) had a higher filling rate and longer grouting distance than ordinary cement slurry; in grouting experiments conducted on rough single-fissure models produced by 3D printing, the optimal modified slurry exhibited greater activity, diffusion speed, and diffusion area; in seepage tests conducted in the filled fissures formed by grouting experiments, the modified grout resulted in a 15 % increase in the Darcy factor and a 31.5 % decrease in permeability compared to ordinary cement slurry.