CO₂ pre-fracturing has the characteristics of miscibility, energy enhancement, viscosity reduction, permeability improvement, and complex fracture formation, and is gradually being applied in the development of unconventional oil and gas. The phase behavior during CO₂ injection significantly affects the performance of CO₂ pre-fracturing. However, the heat transfer and frictional resistance changes of CO₂ in the wellbore are complex, and the prediction of the CO₂ phase transition depth is difficult, which restricts the optimization of CO₂ injection parameters. The Span-Wagner state equation was coupled with the wellbore flow-heat-transfer-pressure drop model, the physical property changes of CO₂, various heat transfer mechanisms and flow pressure drop mechanisms were comprehensively considered, and a CO₂ pre-fracturing wellbore temperature and pressure prediction model was established. The accuracy of the model was verified by using the measured temperature and pressure data of the CO₂ injection well. Taking the typical well of CO₂ pre-fracturing in Mahu as an example, the effects of injection parameters on the temperature-pressure distribution and phase transition depth of CO₂ in the wellbore were systematically revealed. The results show as follows. The wellbore temperature increases with the increase of the CO₂ injection temperature and decreases with the increase of the injection pressure and injection volume. When the well depth is greater than 2 500 m, the wellbore CO₂ temperature is not significantly affected by the injection temperature at the wellhead.The wellbore pressure increases with the increase of the injection pressure and is not significantly affected by the injection volume and injection temperature of CO₂.The bottomhole pressure increases with the increase of the CO₂ injection rate. When the rate is lower than 1.2 m³/min, the hydrostatic pressure dominates, and the bottomhole pressure increases with the increase of the rate. When the rate is higher than 1.2 m³/min, the wellbore friction dominates, and the bottomhole pressure decreases with the increase of the rate. The model established in this study provides a direct theoretical basis for real-time optimization of CO₂ pre-fracturing injection parameters, precise phase control, and intelligent decision-making for field operation plans, and is of great significance for improving the stimulation effect and engineering economic benefits of CO₂ pre-fracturing in unconventional oil and gas reservoirs.