Performance of freezing and refrigeration systems in supermarket, which utilized CO2 as a refrigerant, was investigated by using the Pack Calculation II. The configuration of simulated systems was basic parallel refrigeration system, cascade system, and two-stage system. The CO2 cascade system showed higher COP than basic parallel R404A system by 13% for MT and 62% for LT, respectively. Among the CO2 cascade systems, R717(MT)-CO2(LT) showed the highest performance. Open-type intercooler method showed higher performance than liquid injection for the two-stage CO2 systems.