At temperatures greater than 70 degrees C, the introduction of air in the slurry preparation process in slag hydration of solidified stone produces cracking and thermal stresses. In the study, slag cementing slurries at 90 degrees C were used to join brucite fibers. The mechanical performance, toughening mechanism, and microstructural changes were studied using tensile tests, XRD, TGA, SEM, IR, and triaxial tests. After curing for 14 and 28 days, the compressive and tensile strengths of 6 wt% brucite fiber-reinforced slag increased by 69.08 and 45.98% and 73.58 and 69.08%, respectively, while the elastic modulus decreased 8.4% compared to the control samples The brucite fibers were randomly distributed in the slag cementing slurries, resulting in a toughened material via energy dissipation caused by bridging peel and pulling-out. This result provides theoretical background to solve strength attenuation and cracking phenomenon at high temperature in solidified slag stones.