Abstract: Cement is one of the main materials for grouting in underground engineering, and its setting time and rheological properties play a key role in the engineering. Aiming at the issue of long setting time of cement slurry, this paper takes P·O 42.5 cement as the matrix, incorporates 2%-8% of alkali-free accelerator based on aluminum sulfate, and selects cement slurries with water-to-cement ratios of 0.6, 0.8, and 1.0 for initial setting time, rheological properties, and fracture grouting tests. The results show that for every 1% increase in the dosage of alkali-free accelerator, the initial setting times of slurries with different water-to-cement ratios are shortened by 11.4%, 3.9%, and 3.6%, respectively. The initial shear stress τ₀ of the rheological curve increases by 10% with the increase in the dosage of alkali-free accelerator. The Herschel-Bulkley rheological model was used to characterize the rheological behavior of the slurry. The shear stress τ₀ is linearly related to the hydration time t, with a slope of (30± 3) Pa/min. The consistency coefficient K has a linear relationship with the hydration time t, with a slope less than 0.003 333 Pa·s^n-1. To investigate the diffusion range and laws of the slurry with alkali-free accelerator, the grouting diffusion laws were quantified through fracture grouting experiments, and the radius prediction formula was determined. The growth coefficient of the diffusion radius is 200 ± 40, and the diffusion radius growth rate is 0.57 ± 0.3. Based on the comprehensive experimental results, the mixture proportion with a water-to-cement ratio of 0.6 and an alkali-free accelerator dosage of 3%(A2) is recommended for rapid water blocking, and the mixture proportion with a water-to-cement ratio of 1 and an alkali-free accelerator dosage of 8%(C2) is recommended for deep-penetration grouting.