Abstract: To investigate the effect of CO₂ fracturing on the pore structure of coal rock，mercury po⁃ rosimetry and scanning electron microscopy experiments were conducted，combined with thermodynamic fractal models and island fractal models. The modified effect of fracturing on pores and the evolution of fractal dimension were quantitatively analyzed. Based on the fractal intersection formula，the comprehen⁃ sive fractal dimension was calculated. The influence of weak heterogeneity and damage mode transforma⁃ tion on pores was explored. The results showed that after fracturing，the pore volume，average pore diame⁃ ter，and porosity all increased by 2~3 times compared to the original coal，and the specific surface area also increased simultaneously. The pore size distribution indicated that small，medium，and large pores （>10 nm）developed simultaneously，especially forming ink-bottle type pore structures in the range of 10~100 000 nm. The pore size distribution measured by scanning electron microscopy showed a significant increase in pore volume，equivalent circular diameter，and average pore area. The decrease in fractal di⁃ mension indicated that the pore surface became smoother and the heterogeneity weakened; the damage mode shifted from mixed failure（tensile-shear）to single shear dominance，and the permeability signifi⁃ cantly increased.

Key words: coal and gas outburst, CO2 fracturing, mercury porosimetry, scanning electron microsco? py, fractal dimension