Abstract: The utilization of coalbed methane (CBM) cannot only alleviate the energy crisis, but also reduce greenhouse gas emissions. Gas injection is an effective method to enhance CBM recovery. Compared to single-gas injection, the injection of CO2/N2 mixtures can balance the sharp decline in permeability caused by pure CO2 and the premature breakthrough by pure N2. In this study, a more comprehensive thermo-hydro-mechanical (THM) coupled mathematical model was developed, incorporating processes such as ternary gas non-isothermal adsorption, gas dissolution in water, gas–water two-phase flow, energy exchange, and coal deformation. After experimental validation, the model was applied to simulate the entire process of gas mixtures for enhanced CBM recovery (GM-ECBM). Results indicate that the permeability near the production well (PW) initially decreases due to increased effective stress, then increases as a result of CH4 desorption. Near the injection well (IW), the permeability first increases due to reduced effective stress and later stabilizes under the combined effects of effective stress and CO2/N2 adsorption. The initial CH4 pressure and coal seam permeability have the most significant impact on CH4 production, while the coal seam permeability and temperature significantly affect CO2/N2 injection. As the coal seam permeability increases, the optimal CO2/N2 ratio also increases accordingly. These findings provide important theoretical guidance for improving GM-ECBM efficiency in coal seams with varying permeabilities.