Abstract: Geological CO₂ storage in coal seams is one of the key technologies for achieving the “carbon peak and carbon neutrality” goals, with potential assessment and leakage mechanism research holding significant importance for engineering practices. Taking Kongzhuang Coal Mine as a case study, this paper employs the fuzzy comprehensive evaluation method to assess the CO₂ storage stability of its No.7, No.8, and No.17 coal seams. An evaluation system containing 7 primary indicators and 1 secondary indicator is established. Through coal rock quality characteristic testing and comprehensive evaluation results, numerical simulation methods are applied to clarify the multi-coal seam fault leakage mechanisms. The research demonstrates that the No.7, No.8, and No.17 coal seams exhibit high CO₂ storage potential, all rated as “relatively stable” and suitable for CO₂ storage of multi-coal seams. The results of the comprehensive evaluation of the stability of each coal seam are 90.794, 91.587 and 93.273 respectively, and the sealed amount is 120.27 Mt, 30.89 Mt and 14.78 Mt in order. Based on evaluation outcomes and geological conditions, the coal seams are classified into three storage feasibility zones: favorable, moderately favorable, and unfavorable. Numerical simulations reveal that when the FC8 through-fault remains unsealed, CO₂ migration rate and plume dispersion accelerate in upstream areas, while sealing the fault leads to increased migration velocity and rapid plume diffusion in downstream regions. Therefore, the optimal timing for through-fault sealing in practical projects should be: ceasing CO₂ injection when migration reaches the upstream-downstream demarcation point, followed by immediate fault sealing to prevent leakage. This approach effectively enhances CO₂ dispersion efficiency while reducing storage costs and leakage risks. The findings provide theoretical guidance for implementing CO₂ storage projects of multi-coal seams in coal mines.