Abstract: Backfill in key zones serves as a crucial approach for reconstructing underground carbon storage spaces and represents a scientific measure for the large-scale disposal of alkaline solid waste along with carbon emission reduction. Based on a mix proportion of cement∶red mud∶fly ash∶bauxite slag = 1∶3∶1∶6, a tailing-based cemented paste backfill (TCPB) material with a solid-to-liquid ratio of 4∶1 was prepared. Carbonation curing tests under different CO₂ pressures were conducted using a self-designed carbonation test system. The carbon storage rate of the backfill was calculated by the gravimetric method, and the carbonation depth was quantified via the phenolphthalein staining method. Characterization techniques such as X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscopy (SEM) were employed to reveal the hydration–carbonation reaction mechanism of TCPB under different carbonation curing pressures and to clarify the influence of carbonation curing pressure on the carbon storage and bearing capacity of the backfill material. The results indicate that increasing the CO₂ curing pressure accelerates the carbonation process and efficiency of TCPB. Under 1 MPa carbonation curing pressure, the carbon storage capacity of TCPB reached 36.5 kg/t. The strength of TCPB specimens decreased with increasing carbon storage, due to the consumption of alkaline substances originally involved in hydration reactions, which were gradually converted via carbonation, leading to a reduction in the formation of C–S(A)–H gel—the primary source of strength. Compared with non-carbonated specimens, the strength deterioration of carbonated TCPB backfill specimens after 28 days of continued curing can be limited to 7.5%, demonstrating that TCPB maintains satisfactory bearing capacity after carbon sequestration and meets the requirements for field backfilling applications. According to assessments of the total volume of underground goaf spaces in Chinese coal mines, the application of TCPB materials for goaf backfilling could consume 2.67 billion tons of red mud, 0.89 billion tons of fly ash, and 5.34 billion tons of bauxite slag, while sequestering 0.45 billion tons of CO₂. Therefore, using TCPB materials for goaf backfilling and reconstruction can simultaneously achieve low-carbon, large-scale utilization of solid waste, thereby providing a theoretical basis and scientific support for the low-carbon treatment and functional enhancement of goaf areas.