Mixtures of CO2 and HCs may be promising refrigerants since they can contemporarily reduce the problems connected to high operating pressure of CO2 and the flammability of HCs. In this paper, system performance of CO2+Ethane mixture were evaluated and discussed as working fluids for a cascade refrigeration system. In a refrigeration system using azeotropic mixture, there is still a difference between the refrigerant’s charged concentration and its circulation concentration. There is a difference between the charging refrigerant composition into the system with the refrigerant circulated in the cascade refrigeration system. Although the differences are not so high, the mixture tends to be a zeotrope refrigerant. At the discharge and suction line where the mixture considered as gas phase, the mixture composition is in close proximity to charging and azeotrope composition. In contrast to the liquid phase, the composition CO2 is less than the initial composition of the charging and azeotrope mixture. It is because the CO2 in liquid phase is more volatile than Ethane and also due to the practical operating conditions and hardware of system.