Aiming to address the environmental problems in the reclamation process of coal gangue in mines in the arid region of Northwest China, especially the high risk of heavy metal Cd precipitation and spontaneous combustion of coal gangue, this paper proposes a new idea of environmentally friendly modified solidified soil (MSS) to enhance the synergistic disposal of geotechnical and environmental safety in the reconfiguration of the soil of the gangue.The MSS is made of 78.9 % silt soil, 15.1 % fly ash, and 6 % standard cement prepared with 4.5 % modified polyacrylamide (MPAM) to form solidfied soil. MSS filling the pores of coal gangue pile to form coal gangue-MSS(CG-MSS)backfill has double advantages: the curing efficiency of MSS on Cd2+ in gangue reaches 76.9 % (12.5 % for untreated gangue), and reducing the leaching concentration to 0.21 mg/kg (<0.3 mg/kg, GB15618-2018); Moreover, the CG-MSS composite exhibited markedly improved thermal stability, with a thermal decomposition threshold elevated to 605.0 degrees C, an increase of 354.4 degrees C compared to raw gangue, and maintained a low self-heating rate of 0.08 degrees C/min, substantially inhibiting spontaneous combustion. The microstructure analyses reveals the environmental enhancement mechanism of MSS for gangue reclamation: (1) the pore structure of CG-MSS is more homogeneous and dense (the lowest porosity is 0.091, which is 90.27 % lower than that of the pure gangue); (2) the mobile cadmium in the gangue is solidified through the adsorption of calomel and C-S-H encapsulation; (3) MSS forms an oxygen-barrier layer on the surface of the gangue via its hydration products. MSS technology has significant cost-effectiveness and sustainability advantages (52.8 % and 16.7 % reduction), can completely replace the traditional cement-based backfill materials, enhance the ecological and environmental benefits of the mining area, reduce the cost of traditional land reclamation, and is expected to promote the large-scale ecological utilization of coal gangue in the Northwest and sustainable reclamation of the mining area.