The extraction of magnesium by prefabricated pellets with CaSi₂ as reductant was studied under relative vacuum. The morphologies, chemical compositions and phases of the reduction slag were analyzed using scanning electronic microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD), respectively. The results showed that a small amount of argon flow could greatly improve the reduction rate of MgO. The process of extracting magnesium from prefabricated pellets under relative vacuum could be well explained by Model F₁. The process of reducing magnesium oxide by CaSi₂ was a solid-liquid reaction. This process was controlled by chemical reaction, the temperature had a great influence on the reduction reaction, and the value of the apparent activation energy was 108.99 kJ/mol. The phase analysis of reduction slag showed that the content of MgO had an effect on the crystal transformation of Ca₂SiO₄.