The work aims to study the schemes and type selection design of 25 aquatic product quick-freezing warehouses at -30 ℃ and 4 aquatic product low-temperature refrigerators at -25 ℃, and find out the best refrigeration system optimization design scheme. Based on the advantages of CO2 refrigerant such as green, high efficiency and energy saving, R507/R744 cascade refrigeration system was proposed for the freezing and refrigeration of aquatic products with the CO2 compressor parallel technology. When the evaporation temperature was -30 ℃, different refrigerants were selected and the BITZER compressor software were used to study and calculate the refrigeration efficiency (COP) of different systems, and the COP and economy of different refrigeration systems were analyzed. Compared with R507 refrigeration system, the COP of the cascade system was increased by more than 10%. The average annual electricity cost of the cascade system as a whole was over 50% less than that of the domestic ammonia refrigeration system. At the same time, setting the backup motor and the main safety valve was put forward for the safety problems that needed to be emphasized in such engineering applications. In the aquatic product refrigeration, the comparison of cooling efficiency and annual power consumptions of different refrigeration systems indicate that, the R507/R744 cascade refrigeration system selected is featured by higher refrigeration efficiency and less annual power consumptions.