In order to accurately predict the phase change of fluids in the process of fracturing and provide effective guidance for the design of field CO2 fracturing, this paper took Well SH52 in a tight sandstone gas reservoir of the Shenmu Gas Field, Ordos Basin, as an example to establish a wellbore-formation coupling numerical simulation model using the commercial software CMG. Then, a reliable numerical simulation model was obtained by fitting the fracturing performance of Well SH52. Finally, the whole process of CO2 injection–fracturing–flowback was simulated, and the phase behavior of fluids in the whole process of CO2 fracturing and the effects of fracturing technological parameters on the bottom-hole pressure, temperature and fluid PVT at the end of CO2 injection were investigated. And the following research results were obtained. First, in the whole fracturing process from injection to flowback, CO2 undergoes a phase change process of "liquid state–supercritical state–liquid state–gas state". In the process of CO2 injection, fracture initiation and fracture extension, CO2 changes from the liquid state to the supercritical state and its density changes greatly in the range of 800–1 100 kg/m3. Second, at the end of CO2 injection, with the increase of the total CO2, the bottom-hole temperature decreases gradually, while the bottom-hole pressure and the bottom-hole CO2 density and viscosity increase gradually. Third, CO2 displacement rate is overall similar to the total CO2 in the influential laws on the bottom-hole temperature, pressure, CO2 density and CO2 viscosity, except that the influence of CO2 displacement rate on the bottom-hole pressure is greater. Fourth, when the total CO2 is more than 400 m3 or the CO2 displacement rate is more than 4 m3/min, their influences on the bottom-hole temperature, pressure, CO2 density, and CO2 viscosity are no longer obvious. In conclusion, by virtue of this proposed model, the phase behavior of fluids in the process of CO2 fracturing can be predicted accurately with higher fitting precision. It is indicated that this model is reliable. And the research results provide a technical support for optimizing the design of CO2 fracturing.