Liquid CO2 phase transition blasting is a physical blasting method to enhance permeability through liquid CO2 phase transition expansion. To study the propagation criterion of fractures during blasting, the energy of phase transition blasting is evaluated through the thermodynamic equation by studying the action process of the liquid CO2 blasting, thus obtaining the scope of the smash zone and crack zone as well as the propagation criterion of fractures under the effect of high pressure gas. The gas blasting model for a coal body is established based on the SPH algorithm, thus obtaining the criteria for formation of the smash zone and for generatio and propagation of the crack zone. Moreover, the radius of phase transition blasting is surveyed onsite by the peephole method. It is shown that the explosive energy of the MZL-51/2000 phase transition blasting equipment with a release pressure of 270 MPa is 1510 kJ. The coal body is crushed by the high pressure CO2 percussive drilling, forming the smash zone. Meanwhile, fractures are generated around the smash zone. With the expansion and migratio of the gas, the fracture will further grow into a crack zone. The fracture inside the coal body goes through four states: rapid, slow, rapid, and then slow again. According to field surveys, the blasting radius of the MZL-51/2000 equipment with loaded liquid of 1.8 kg is approximately 3 m.