Abstract: To elucidate the complex phase-change mechanisms within high-temperature hydrocarbon fuel pressure swirl nozzles in aerospace propulsion systems, a non-isothermal numerical simulation framework was established based on an improved Zwart cavitation model. The flow characteristics of the pressure swirl nozzles were systematically investigated over a temperature range of 333-543 K and a pressure differential range of 0.3-3.0 MPa. It was found that the ratio of the Jakob number to the cavitation number (Ja/Ca) serves as an effective dimensionless parameter to delineate three distinct flow regimes: cavitation dominated (Ja/Ca＜0.2), strongly-coupled transition(0.2≤Ja/Ca≤0.5), and flash-boiling dominated (Ja/Ca＞0.5). A critical transition temperature of 460 K was identified. Above this threshold, vapor choking caused a maximum reduction of 76% in the flow coefficient. Increasing the pressure drop not only expanded the low-pressure region but also significantly modulated the competition between cavitation and flash boiling. A critical temperature prediction model based on the Ja/Ca criterion was developed, providing a dimensionless characterization of the coupled thermodynamic and hydrodynamic effects, with a prediction error of less than 5%. This study provides a quantitative basis for the thermal management design and operational boundary definition of high-temperature propulsion systems.