Relying on the R404A/R23 cascade ultra-low temperature refrigeration test bench, and using the method of controlling single variable, the evaporation temperature and condensation temperature of the compressor compression ratio, exhaust gas temperature, suction pressure and refrigerant flow rate in the cascade refrigeration cycle were studied. The effect of the refrigeration coefficient. The results showed that when the evaporation temperature was reduced from -50 ℃ to -55 ℃, the system refrigeration coefficient declined the fastest, reaching 2.1%; when the condensation temperature was raised from 28 ℃ to 30 ℃, the system refrigeration coefficient declined the fastest, with 1.7%. And the evaporation temperature dropped by 1 ℃ and the condensation temperature rised by 1 ℃, which had a greater influence on the system performance coefficient. In addition, when the evaporation temperature was -55 ℃, and the condensation temperature was 36 ℃, the compressor discharge temperature reached a maximum of 90 ℃. At this time, the system performance coefficient was at least 1.5, so effectively control the compressor discharge temperature to the system safety and efficient operation is essential.