Abstract: According to the problems of complicated geological tectonics, high tectonic stress, poor seam permeability and poor gas drainage effect in Baijiao Mine, a permeability improved technology combined with a high pressure hydraulic fracturing and carbon dioxide phase change cracking was provided and the principle of the hydraulic fracturing and carbon dioxide combined permeability improved technology was analyzed. A comparison experiment study was conducted on the combined per meability improvement of No. B4 Seam in No. 238 floor gateway. The experiment results showed that the permeability of the seam in the technical experiment area was remarkably improved and the initial drained gas volume fraction of a single borehole was 1.70 times and 3.48 times higher than the average volume fractions of the high pressure hydraulic fracturing area and the conventional gas drainage trial area individually. The gas drainage pure volume was improved by 1 .49 and 3.04 times higher than the hydraulic fracturing area and the conventional gas drainage area individually. After 65 days of the gas drainage operation, the total gas volume fraction of the h igh pressure hydraulic fracturing and carbon dioxide phase change cracking combined permeability area could keep over 40%, the gas drainage effect was excellent an d the technology could provide references to the similar mines.