Abstract: In the process of CO₂-enhanced coalbed methane recovery, the behaviours of coal seam fractures significantly affect sequestration and extraction. To address the unclear impact of fracture roughness evolution on engineering efficiency under multi-physical field coupling effects, we developed an innovative interdisciplinary mathematical model. This model introduces a parameter to quantitatively describe coal seam fracture roughness and couples it with the gas flow control equations under multi-field effects in the coal seam. We investigated the thermo-hydro-mechanical (THM) coupling effects and fracture network characteristics in the coal seam gas extraction process. Results show that the mathematical model aligns well with field data and effectively characterizes coal seam fracture roughness. Fracture roughness significantly influences the residual gas pressure in the coal seam and the injection pressure of CO₂. When the roughness parameter decreases from 0.24 to 0.18, the maximum methane content decreases by 32.5% and the maximum CO₂ pressure increases by 26.7%, the maximum gas adsorption capacity of coal seam decreased by 31.7%, and the maximum CO₂ adsorption capacity increased by 12.1%.