Abstract: Natural gas hydrate resources are distributed in deep-sea sediments and permafrost layers under high-pressure and low-temperature conditions. CO₂ fluid is widely applied in various unconventional oil and gas drilling and extraction projects. However, there is a lack of systematic research on the characteristics and modulation methods of liquid CO₂ jet flow in the downhole environments during the drilling and completion processes. The paper establishes a CO₂ fluid phase transition model controlled by cavitation and heat transfer, conducts comparative analyses on the jet velocity and vapor phase distribution characteristics of conical nozzles, convergent-divergent cavitation nozzles, and self-resonating cavitation nozzles under the downhole pressure and temperature conditions of hydrate wells, and investigates the influence of CO₂ fluid temperature on jet mass flow rate, axial velocity, and vapor phase distribution. The results show that the phase transition of liquid CO₂ jets and the formation of Mach disc structures can be inhibited under the low-temperature and high-pressure conditions at the bottom of natural gas hydrate wells, and significant self-excited pulsation phenomena exist in the flow field. The cavitation clouds formed by the three nozzles exhibit strip-shaped, fan-shaped, and spindle-shaped patterns, respectively. Compared to conventional water jets, liquid CO₂ jets can achieve higher jet velocity under lower energy consumption. The CO₂ fluid temperature has limited effects on jet mass flow rate, axial velocity, and vapor phase evolution cycles, but significantly affects the vapor phase distribution range. By contrast, convergent-divergent nozzles have faster jet velocity and stronger cavitation effect. Increasing the fluid temperature can suppress the self-excited pulsation phenomenon of jets and promote cavitation in the external flow field.