High-flow low-expansion backfill materials have been developed to improve difficult slurry pipeline transport and the poor roof-contact effect of many filling materials. The fly ash content was fixed at 80%, and the content of mineral powder was 8.5% - 9.5%, lime was 8.5% - 9.5%, and desulfurized gypsum was 2% - 3%, with a sodium carbonate content of 0.9% - 1.2% and an aluminum powder content of 0.01% - 0.02%. The prepared backfill material processed good fluidity, and the expansion rate of the hardened material reached 2% - 3%, and the compressive strength at 90 d reached 4 MPa - 5.5 MPa. SEM observations indicated that as the aluminum content increased, the ettringite on bubble walls transformed from a fine-needle to a needle-rod shape. Secondly, the hydration products of the system were mainly hydrated calcium silicate gel and ettringite, which interconnected and promoted the formation of the structure. The backfill material had extensive sources of raw materials, low cost, and a simple filling process and good filling effect.