To address the issues of high cost and poor low-temperature adaptability in cement-based backfill materials, this study developed a high-volume fly ash-based solid waste cementitious backfill material (FAPB) along with a specialized low-temperature admixture. Investigated the fundamental properties and microscopic curing mechanisms of the FAPB at different temperatures. The results indicate that the yield stress and plastic viscosity of FAPB slurry increase with higher contents of the curing agent and admixture, and rise as the temperature decreases. The variation in slump flow aligns with the rheological parameters, with the minimum slump flow being 14.5 cm (>10 cm). Bleeding rate increases with decreasing amounts of curing agent and admixture content, as well as lower temperatures, reaching a maximum bleeding rate of 9.26% (T5C10). Setting time decreases with increased amounts of curing agent and admixtures, and significantly increases with decreasing temperature. Strength increases with curing time and curing agent content, but decreases significantly as temperature drops. Adding admixtures can compensate for strength deterioration caused by low temperatures, with an optimal dosage of 3%. Microstructural analysis showed that the main hydration products of hardened backfill include AFt, C-S(A)-H, and Ca(OH)₂. Low temperature (5 °C) restricts hydration product formation, and the admixture facilitates continuous polycondensation of C-S(A)-H gel, resulting in sustained strength gain. This study provides a theoretical basis for the preparation and application of low-temperature-resistant Fly ash-based backfill materials, holding significant importance for advancing green mining practices in cold regions.