<p>This study systematically investigated the parameter optimization for the vacuum thermal reduction process of calcined magnesite using Al–Si alloys. The primary objectives were to achieve a reduction degree of magnesium comparable to or higher than that of the conventional Pidgeon process by optimizing the reaction temperature, slagging agent CaO addition, and aluminum content in the alloys. The results revealed that increasing the reduction temperature and aluminum content in the alloys significantly enhanced the reduction degree of magnesium. The appropriate addition of CaO effectively activates the reduction potential of silicon in the alloys, enabling silicon to participate in the reduction reaction at lower temperatures, thereby improving silicon's reduction efficiency. Moreover, the catalytic effect of CaO is more pronounced in alloy systems with higher silicon content. Additionally, the introduced CaO combines with SiO₂ or Al₂O₃, effectively inhibiting the incorporation of MgO into the slag phase and reducing the loss of reduction degree. Under conditions at 1150 °C and a CaO/MgO molar ratio of 0.5, both AlSi50 and AlSi30 alloys achieved a reduction degree exceeding 80 pct, which was only about 4 pct lower than that of the pure aluminum system. The dual reduction in smelting temperature and aluminum content in the reductant implied that smelting costs can be significantly lowered. Meanwhile, the optimization of slagging agents also substantially decreased the amount of slag generated during the process.</p>