Abstract: In order to promote gas drainage in low-permeability coal seams, implement the optimization of enhancing permeability and promoting gas drainage technology by liquid CO₂ injection into freeze-thaw cracked coal seams, taking Changcun Coal Mine as the research background, using nuclear magnetic resonance, ultrasonic detection and other methods, the evolution of coal pore structure and damage mechanism under different freezing times of liquid CO₂ are analyzed. The research results show that the macroscopic cracks of the coal sample gradually change significantly after freezing and thawing for 50 minutes. With the increase of the fracture time, the shear and longitudinal waves of the coal body gradually decrease, and the reduction rates of longitudinal and shear waves are in the range of 5.55% to 34.33% and 3.72% to 17.44% respectively; pores of various sizes in the coal body gradually develop, and the growth rate of full-pore T₂ spectrum area increased from 28.67% to 61.49%, and the pore connectivity of the coal body was strengthened, which was conducive to improving the permeability of the coal body.