The slurry-rock mass coupling effect significantly influences the grouting process in micro-fissured rock. Existing research predominantly focuses on the grouting diffusion stage, often neglecting the pressure dissipation stage, leading to inaccurate predictions of diffusion range and pressure distribution. This paper presents a theoretical model and a step-wise calculation method for grouting diffusion and pressure dissipation in a single parallel-plate micro-fissure, accounting for the slurry-rock mass coupling effect. The interaction mechanism between the surrounding rock elastic rebound and the time-dependent yield stress of the slurry during pressure dissipation is revealed. The formation mechanisms of residual slurry pressure and residual fissure deformation are clarified. The calculation results are verified by the data in the grouting project of Qingdao Metro in China. Results demonstrate that neglecting the coupling effect may overestimate the injection peak pressure by 5 times and underestimate the diffusion radius by 2 orders under high injection peak pressure. During the grouting diffusion stage, the peak injection pressure for a smaller initial fissure aperture (0.2 mm) is nearly twice that of a larger one (0.5 mm). At low injection peak pressures (0–3 MPa), the slurry volume absorbed by fissure deformation is below 2% for b₀ ≥ 0.4 mm; however, at 10 MPa, the proportion for b₀ ≤ 0.3 mm is nearly twice that for b0 ≥ 0.4 mm. During the pressure dissipation stage, the residual pressure difference reaches 3 times. While the rock mass elastic modulus correlates positively with injection pressure and negatively with fissure aperture, its influence during pressure dissipation is minimal (merely 6% injection pressure difference and 5% maximum aperture difference between E = 80 GPa and E = 20 GPa). In the Qingdao Metro grouting project, the calculated injection pressure differs from in-situ measured values by 5%–20% in the diffusion stage and 10%–15% in the pressure dissipation stage. This validates the rationality of the theoretical model.