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Although several theoretical calculation methods for high-pressure jet are available, there is currently no theoretical model for the high-pressure CO2 jet based on the high-precision equation of state (EOS). To investigate the flow field of the high-pressure CO2 jet in cases of the composite rock-breaking under the high-pressure CO2 Jet and PDC cutter, a semi-analytical approach of the high-pressure CO2 jet is developed based on the Span-Wagner EOS and CO2 jet theory. The semi-analytical calculations and the physical property calculations under the action of the high-pressure CO2 jet are conducted with consideration of the jet pressure, the jet distance, the nozzle diameter and the jet angle. The results indicate that the distribution of the physical properties calculated by the semi-analytical approaches is similar to that obtained by experimental monitoring and numerical simulation, which indicates that the calculation method of the high-pressure CO2 jet presented in this paper is effective and reliable. The properties of the CO2 jet obtained by the theoretical calculation see a significant difference between the initial region and the jet impact region. At the temperature of 300 K, the increase of the initial pressure can effectively increase the impact force and the cooling ability of the jet. The proportion of the jet core lengths in the jet on the axis increases with the increase of the ratio of the nozzle diameter to the jet length, accompanied with the increase of the impact force of the jet. The increase of the jet angle can effectively increase the impacting force of the jet, but hampers the fluid diffusion. The study combines the theoretical calculation of the jet with the calculation of the physical properties of the high-pressure CO2, for comprehensively understanding the CO2 jet field in the composite rock-breaking under the action of the high-pressure CO2 jet and PDC cutter. This theoretical calculation of the CO2 jet based on the high-precision EOS provides an option for the convenient calculation of the CO2 drilling in practical engineering. [ABSTRACT FROM AUTHOR]