The freeze-drying of plasma typically requires a low-temperature environment of ?50 ℃, which is currently realized by R404A/R23 cascade refrigeration systems. However, this working fluid combination possesses a high global warming potential, which fails to conform to the development trend of green and low-carbon refrigeration technology. This study adopted a low global warming potential R450A/R170 refrigerant combination and analyzed the performance of R404A/R23 and R450A/R170 cascade systems based on thermodynamic energy analysis, exergy analysis, and carbon emission analysis models. The results show that under the optimal intermediate temperature condition at a condensation temperature of 45 ℃, the coefficient of performance and exergy efficiency η of the R450A/R170 system are improved by 8.40% and 5.68%, respectively, compared with the R404A/R23 system. Meanwhile, the total compressor power consumption and total exergy loss are reduced by 7.73% and 11.92%, respectively. Within the condensation temperature range from 35 ℃ to 45 ℃, the coefficient of performance and η of the R450A/R170 system remain consistently superior, with a lower decline rate as the condensation temperature rises, indicating that the system has stronger adaptability to variations in operating conditions. Exergy analysis reveals that low-temperature and high-temperature stage compressors are the components with the largest exergy loss, presenting considerable optimization potential. Under the same cooling capacity, the R450A/R170 system requires a smaller displacement of the low-temperature stage compressor but a larger displacement of the high-temperature stage compressor. At a condensation temperature of 45 ℃, the direct and indirect carbon emissions of the R450A/R170 system are significantly reduced by 95.87% and 7.75%, respectively, relative to the R404A/R23 system, leading to a 36.40% reduction in total carbon emissions. This study demonstrates that the R450A/R170 cascade system outperforms the traditional system significantly in terms of energy efficiency, operating adaptability and environmental performance, which provides a reliable theoretical basis for refrigerant replacement and system optimization in the field of low-temperature preservation of biological samples.