Due to lightweight, high-strength, and high toughness properties, Basic magnesium sulfate cement (BMSC) can be widely used in producing various structural and decorative products. Most current research only focuses on the performance of BMSC under room temperature. However, low temperature environments may have a serious impact on the performance of BMSC, such as during cold seasons or in salt lake cold regions with abundant magnesium resources, so the performance of BMSC in low temperature environment needs to be explored to expand its application. This study investigated the influence of different low temperatures (−5 to 20°C) on the compressive strength and water resistance of BMSC cement. The phase composition, microstructure and pore structure of BMSC has been analyzed using XRD, QXRD, TG/DTA, SEM, BSEM/EDS Mapping and MIP. The Results indicate that the low hydration rate, precipitation of magnesium sulfate, increase in porosity and decrease in 517 phase content are the main reasons for the low strength of BMSC under low temperature curing. Although hardened BMSCs cured at low temperatures can continue to hydrate in water to form strength phases, corrosion and cracking may occur. Replacing light burned magnesite with high active magnesium oxide can significantly improve the mechanical properties of low temperature cured BMSC. However, low temperatures reduced the crystallinity of the 517 phase, thereby increasing its water solubility and lead to poor water resistance of BMSC.