Due to the high GWP value (global warming potential) of R404A refrigerant which is widely used at present and unfriendly to the environment, it has been increasingly urgent to find a suitable low GWP refrigerant. In order to explore the effect of new alternative refrigerant with low GWP value on the performance of refrigeration system, the thermodynamic model of cascade refrigeration system was established, and the performance of the new alternative refrigerants R455A and R448A with low GWP value under different working conditions was studied. These results were compared with the R404A system in terms of evaporation temperature of low temperature stage, condensation temperature of high temperature stage, interstage temperature and subcooling degree of high and low temperature stages. The results indicate that the COP (coefficient of performance) of R455A/R23 system is always the highest and the COP of R404A/R23 system is the lowest under different working conditions. Under the same evaporation temperature, the optimum interstage temperature of R455A/R23 and R448A/R23 system is lower than that of R404A/R23 system. The optimum COP of R455A/R23 and R448A/R23 system is 6.77% and 5.25% higher than that of R404A/R23 system. In addition, the increase of high temperature level undercooling will increase the COP of cascade system. The increase of COP in R404A/R23 system is the largest, and the increase of COP in R448A/R23 system is the smallest.The increase of low temperature level undercooling will degrade the system performance.