This work studies the performance of CO2-based mixture refrigerants in GSHPs with ejector. R41, R32, R161 and R1270 are selected from different HFC/HFO/HC to be blended with CO2. These mixtures are compared for GSHPs with and without ejector under various compositions. Simulation results indicate that the cooling capacity of each mixture increases with the CO2 mass fraction; ejector increases the cooling capacities for CO2/R41 but decreases those for CO2/R32, CO2/R161 and CO2/R1270. Ejector increases the COP of pure refrigerants and mixtures with small temperature glides, but decreases the COP of mixtures with large temperature glides. Without ejector, mixtures always perform better than CO2 and perform better than pure HFC/HFO/HC under lower CO2 fractions. With ejector, mixtures perform better than CO2 under lower CO2 fractions but never perform better than pure HFC/HFO/HC. In addition, the discharge temperature with ejector is much higher for mixtures with large temperature glides.