Abstract: To achieve the synergistic development of high-value utilization of coal-based solid waste and CO2 mineralization sequestration, a coal gangue-based carbon-sequestering backfill material system was developed using coal gangue, carbide slag, and cement as raw materials. The backfill materials were prepared through a wet mineralization method using a self-developed wet carbonation experimental system. An L16(43) orthogonal array test was employed to investigate the effects of the solid-liquid ratio, coarse-to-fine aggregate mass ratio, and CO2 flow rate on the performance of the materials. A weighted comprehensive evaluation method based on range standardization was adopted to screen material mix proportions with superior engineering applicability. Furthermore, thermogravimetric analysis (TG-DTG), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were conducted to elucidate the mineralization reaction mechanism. The results indicate that the solid-liquid ratio, coarse-to-fine aggregate mass ratio, and CO2 flow rate are the important factors affecting material performance, and their interactions exhibit synergistic effects on material properties. Within the experimental range, the optimal engineering performance was achieved at a solid-liquid ratio of 74%, a coarse-to-fine aggregate mass ratio of 4:6, and a CO2 flow rate of 300 mL/min, under which the 28 d compressive strength reached 10.68 MPa, while the fluidity and bleeding rate satisfied the requirements of mine backfilling engineering. The maximum CO2 uptake of 9.29% was obtained at a solid-liquid ratio of 76%, a coarse-to-fine aggregate mass ratio of 4:6, and a CO2 flow rate of 300 mL/min. Furthermore, the introduction of CO2 promoted the carbonation reactions of hydration products such as C-S-H and calcium-bearing phases, resulting in the formation of CaCO3 that precipitated on particle surfaces and within pores. This process effectively reduced porosity, optimized pore structures, and converted gaseous CO2 into stable mineral carbon, thereby improving the mechanical properties and structural stability of the backfill materials.