Abstract: The large-scale accumulation of industrial solid wastes, including red mud and coal gangue, coupled with goafs left by underground mining activities, poses significant challenges to sustainable human development. In this work, red mud, coal gangue, and other solid wastes are used to prepare underground backfilling material. The utilization rate of total solid waste reaches 95%, with red mud accounting for up to 40%. The unconfined compression strength, setting time, and slump tests are investigated to evaluate the mechanical properties of the material. At the optimal ratio, the 7-day and 28-day strengths reach 4.4 MPa and 6.9 MPa, respectively. The initial and final setting times are 200 and 250 minutes, respectively, whereas the initial and 1-hour slump exceed 250 mm and 210 mm, respectively. XRD, FTIR, and SEM were subsequently employed to explore the microstructure, phase composition, and chemical bonding within the material. Needle-like, cluster, and granular-shaped hydration products are observed, with the primary crystalline structures identified as ettringite, gmelinite, C-A-S-H, and C-S-H. In addition, a thorough environmental risk assessment was conducted, complemented by detailed economic cost and carbon emission calculations. During the creation of a backfill material, hazardous elements from solid wastes are immobilized through adsorption, precipitation, and incorporation into the crystal lattice. The immobilization efficiencies for Ni, Al, Cr6+, and As are 97.03%, 94.32%, 86.43%, and 84.22%, respectively, with the pH maintained at 8.49. Moreover, the use of solid waste as a raw material results in considerable cost savings and a marked reduction in carbon emissions. This research innovatively promotes the green cycle of alumina production and bauxite mining industry.