The paper is based on description of cascade refrigeration systems which are attracting more and more attention in the refrigeration industry, and especially in fields that require very low temperatures. They have wide application like large supermarket chains, rapid freezing of processed food, deep industrial refrigeration, liquefaction of natural gas (LNG), liquefaction of petroleum gas (LPG). All these refrigeration processes require moderately cold refrigeration temperatures in the range of (-30°C to -180°C) with ambient temperature near 20 ° C. This temperature range is too large for a single vapor-compression refrigeration cycle, because it requires a very large pressure ratio across the compressor. In the text, the most attention was paid to cascade refrigeration systems CO2 / NH3 as working substances, due to their good thermodynamic and physical characteristics, they achieve the highest COP of the overall system, compared with other combinations of refrigerants. Usually, CO2 is never replaced, but in a high-temperature circuit ammonia can be replaced with R-410A or R-134a. Also, graphicly is presented the influence of different operating parameters on the overall COP and the optimal condensation temperature of the cascade heat exchanger of the cascade refrigeration system CO2 / NH3 system. Finally, in detail is described cascade refrigeration system(R-1150-R-1270) for reliquefaction of boil of gas (BOG).