Abstract: Using the remaining space of the gob after strip filling to carry out large-scale storage of CO₂ gas is an ideal model to achieve green and low carbon construction in the large coal power base in northwest China. The impermeability of the goaf sealing wall to prevent the horizontal escape of CO₂ gas is the key to the success or failure of this project. Taking the Zhundong II Mine in the Junggar Desertified Mining Area, Xinjiang, as the engineering background. Through high-pressure permeability experiments, phenolphthalein titration experiments, XRD diffraction experiments, SEM electron microscopy experiments and COMSOL numerical simulation, the 28-day permeation process of CO₂ gas at 0.2, 0.4, 0.6, 0.8 and 1.0 MPa in the fly ash sand-based specimens with a mass ratio of 23 (windblown sand)∶11 (fly ash)∶2 (quicklime)∶1 (gypsum) was studied. The results show that: ① The permeation rate of CO₂ gas in the specimens gradually decreases with the permeation time. The permeation depths at 28 days under the five pressures are 1.49, 2.40 , 3.20, 4.0 and 4.77 cm, respectively; ② The porosity and permeability of the fly ash sand-based specimens also show a negative exponential trend of decrease during the CO₂ gas permeation process. The porosity and permeability at 28 days under the five pressures are 30.44% and 5.94×10⁻¹⁵ m², 29.44% and 5.70×10⁻¹⁵ m², 29.03% and 5.57×10⁻¹⁵ m², 28.13% and 5.23×10⁻¹⁵ m², and 27.02% and 4.95×10⁻¹⁵ m², respectively; ③ During the permeation process of CO₂ gas in the fly ash sand-based specimens, needle-like and flocculent CaCO₃ crystals are formed, and the unit cell volume of CaCO₃ is 1.15 times larger than that of Ca(OH)₂, making the specimens more compact; ④ By dynamically assigning the permeability of the material before and after carbonization, it is simulated that the depth distances of CO₂ gas in the fly ash sand-based sealing wall at 3 years under the five pressures are 0.606, 0.921, 1.172, 1.465 and 1.800 m, respectively. Finally, based on the engineering geological conditions of the Zhundong No.2 Mine coal-power base in Xinjiang's desertified mining area, this study focuses on the design of construction process parameters for sealing walls in goaf areas, providing reference for the green mining and low-carbon utilization of coal resources in the desertified mining areas in the northwest of China.