To investigate the feasibility of a CO₂/R1270 mixed refrigerant heat pump system for electric vehicles，the thermophysical properties of the mixed refrigerant were analyzed.A single‑stage transcritical heat pump system model with an internal heat exchanger was established，and the effects of mass ratios and different operating parameters on system performance were examined.The results show that the optimal mass ratio of the CO₂/R1270 mixture is 0.96∶0.04，with the system COP increasing by 13% compared to the single‑refrigerant CO₂ system；the optimal high pressure is 8 MPa，representing a 20% reduction.The refrigeration performance of the system improves as the evaporator inlet temperature rises and decreases as the ambient temperature increases.The impact of changing the evaporator inlet temperature on COP_c is greater than that of ambient temperature.When the ambient temperature is 30 ℃，the COP_c varies most significantly with the evaporation temperature，increasing from 1.18 to 2.81.The most notable factor affecting the system's heating performance is the gas cooler outlet temperature；the system COP_h decreases as the gas cooler outlet temperature rises.Maintaining the gas cooler outlet temperature near the critical temperature of the mixed refrigerant （approximately 42 ℃） yields the optimal heating performance，and the effect of changing the gas cooler outlet temperature on COP_h becomes more pronounced at higher ambient temperatures.This research can provide a reference for the optimal design of mixed refrigerant heat pumps in electric vehicles.