Integrating liquid CO2 phase transition blasting (LCPTB) technology with hydraulic fracturing (HF) methods can help reduce wellbore damage, create multiple radial fractures, and establish a complex fracture network. This approach significantly increases the recovery efficiency of low-permeability oil and gas fields. Accurately calculating the number of fractures caused by LCPTB is crucial to predicting production enhancement effects and optimizing subsequent HF designs. However, few studies have conducted large-scale physical model experiments and proposed a method for calculating the fracture number. This study analyzed the initiation and propagation mechanism of cracks under the LCPTB, derived a calculation formula for crack propagation radius under stress waves, and then proposed a new, fast, and accurate method for calculating the fracture number using the principle of mass conservation. Through ten rock-breaking tests using LCPTB, the study confirmed the effectiveness of the proposed calculation approach and elucidated the variation rule of explosion pressure, the rock-breaking mechanism, and the impact of varying parameters on fracture number. The results show the accuracy and efficiency of the new calculation method, which is particularly suitable for fracturing technologies with high pressure rise rates. Recommendations include enlarging the diameter of the fracturing tube and increasing the liquid CO2 mass in the tube to enhance fracture effectiveness. Moreover, the method can be applied to other fracturing technologies, such as explosive fracturing (EF) within HF formations, indicating its broader applicability and potential impact on optimizing unconventional resource extraction technologies.