Abstract: Aiming at the water hazard threat posed by the burnt rock aquifer in the adjacent fire-damaged zone during the mining of the S1234 working face in Niaotiaota Coal Mine, it is necessary to set a grouting waterproof coal pillar with a certain width on the south side of the working face to block and cut off water inflow from the fire-damaged zone on the south side, thereby ensuring the safe and efficient mining of the working face. To determine the critical safety width of the grouting waterproof coal pillar and improve the recovery rate of the 2⁻² coal seam, a mechanical analysis model of the waterproof coal pillar in the restricted mining zone on the south side of the S1234 working face was established based on the theory of mine pressure. The grouting waterproof coal pillar was divided into an ineffective waterproof zone and an effective waterproof zone, and the influence of excavation disturbance from the haulage gateway and mining disturbance from the working face on the stability of the grouting waterproof coal pillar was considered. Based on the Mohr-Coulomb strength criterion, a method for determining the critical width of the grouting waterproof coal pillar was proposed. The calculation results show that: the widths of the ineffective waterproof zone and effective waterproof zone of the grouting waterproof coal pillar on the south side of the S1234 working face are 5.78 m and 1.55 m respectively, and the theoretically calculated reserved width of the waterproof coal pillar is 7.33 m; the reserved width of the waterproof coal pillar calculated in accordance with relevant specifications is 7.68 m, which is relatively close to the theoretical calculation value. Combined with the actual on-site construction conditions of the S1234 working face, the critical safety width of the waterproof coal pillar was finally determined to be 7.5 m, and grouting reinforcement was carried out on both the ineffective and effective waterproof zones of the coal pillar. The results of the on-site water blocking effect test indicate that: after grouting reinforcement, the water permeability of the coal pillar decreased from moderate to weak, and the permeability coefficient was reduced to (1.7-5.8)×10⁻⁵ cm/s; the specific water inflow of the grouted coal mass decreased to 0.013 9-0.023 6 L/(s·m), a reduction of 50% compared with that before grouting; the water level rise rate of the observation holes decreased significantly, and the variation range of water level difference was reduced, which meets the requirements of on-site production.