Supercritical carbon dioxide (SC-CO2) jet fracturing is expected to be an efficient technique for developing unconventional oil and gas resources. However, when it comes to its feasibility, it is unknown whether SC-CO2 jet fracturing has as much pressure boosting effect in the cavity as the water jet fracturing does and how those parameters affect this pressure boosting effect. In order to answer these two questions, a computational fluid dynamics (CFD) model was formulated in this paper to simulate the flow field in the cavity during SC-CO2 jet fracturing. In addition to the standard CFD models, user defined functions were written to couple the SC-CO2 properties with the pressure and temperature fields. Using this model, the pressure boosting effects of SC-CO2 jet fracturing and water jet fracturing were compared. The results indicated that SC-CO2 jet fracturing had a stronger pressure boosting effect than water jet fracturing because of the lower viscosity of SC-CO2. Moreover, a sensitivity analysis was performed to see the effect of changing the studied parameters on the pressure boosting effect of SC-CO2 jet fracturing. The results indicated that the boost pressure of SC-CO2 jet fracturing increased with the growth of pressure drop and diameter of the nozzle, decreased with the growth of casing hole diameter, and was not affected by annulus pressure and SC-CO2 temperature. This study verified the feasibility of SC-CO2 jet fracturing and provided theoretical basis for the researches and applications of this technique.