An efficient on-board heat pump system can improve the energy utilization rate of new energy vehicles, ensure the safety and reliability of batteries, and reduce the impact of heat pump energy consumption on vehicle range. Given these issues, this paper uses natural refrigerant CO2, a dual-evaporator heat pump system to realize energy cascade utilization, and an ejector to recover the expansion work to improve system efficiency. A hybrid electric vehicle on-board CO2 compression/ejection dual-evaporator heat pump system is proposed, and a heat pump system model is established in the Dymola platform using Modelica language. Through simulation, it was found that under the condition of the ambient temperature of 36°C, when the compressor speed was 4200r/min, the low-temperature evaporator and high-temperature evaporator could provide 4.8kW and 11.76kW of cooling capacity, respectively, with a COP of 7.66.