Abstract: According to the problems of the high gas pressure, the low permeability, the difficult gas pre-drainage at Cheji Coal Mine, the permeability increasing technique tests by CO₂ phase transition fracturing were carried out in the Ⅱ₂ coal seam. The technical principle of CO₂ phase transition fracturing and CO₂ phase transition fracturing device were studied, the influence radius testing programs and the gas extraction effect testing programs of CO₂ phase transition fracturing technique were designed. The field tests showed that, the radius of influence of CO₂ phase transition fracturing test was 4 m, and the average gas extraction flow of the fracturing group was 1.7 times that of the normal extraction group in 15 d.