Two typical types of CO2-NH3 cascade and NH3 two stage compression refrigeration processes were designed and calculated.The key parameters of the two processes were compared

and the heat flow distributions of heat exchangers were also analyzed

as well as parameters optimization of the NH3 refrigeration system.The results show that in terms of evaporation temperature at -45℃

the total power consumption of compressors and NH3 flow of the CO2-NH3 cascade process are less than that of the NH3 process.But there is massive refrigeration capacity at medium temperature in NH3 process

so the COP of NH3 process is higher than that of CO2-NH3 process.The difference in temperature of two phase liquids in the condensation-evaporator of cascade system is less

and that in the midst cooler of NH3 system is larger.Along with the ascending exhaust pressure of low-pressure stage compressor and the descending midst temperature

the total power consumption of the NH3 process of two stage compression will be downtrend.