Cement-sodium silicate (C-S) grout is commonly used as a quick-setting grout, with its performance varying based on temperature. Conventional grouting methods designed for normal temperatures are unsuitable for high-temperature conditions; however, the addition of bentonite can enhance the workability of C-S grout at high temperature. The authors investigate the effects of sodium and calcium bentonite on the rheological and mechanical properties of C-S grout at 20 ℃ and 80 ℃. The mechanisms underlying these effects are analyzed using X-ray diffraction and scanning electron microscopy-energy dispersive spectrometry. The findings are as follows: (1) At 80 ℃, the viscosity and yield stress of C-S grout decrease, while flowability increases. Bentonite enhances viscosity and yield stress while reducing flowability, which helps prevent grout loss during high-temperature water outburst mitigation. (2) Elevated temperature accelerates early strength development in the solidified grout but negatively impacts long-term strength and impermeability. Bentonite modifies the pore structure and decreases porosity, thereby improving impermeability. (3) High temperature promotes the participation of bentonite in late-stage chemical reactions, altering the microstructural properties by optimizing the mineral phase composition of the solidified grout, thereby enhancing the stability of grouting reinforcement over time.