Addressing the issue of low energy efficiency in the compression process of transcritical CO2 refrigeration systems, this study systematically investigates the influence of cylinder cooling on compression efficiency. A numerical model integrating transient heat transfer equations and a modified R-K real gas equation of state was established. The results indicate that increasing the cooling water flow rate from 0.134 m3/h to 0.957 m3/h significantly reduces the compressor discharge temperature by 1.3% ~ 1.7% and compression power consumption by 0.7% ~ 0.9%, with a more pronounced effect observed at lower flow rates. Thermodynamic analysis reveals that increasing cooling water flow reduces the exergy destruction rate, dimensionless constant of entropy generation, and available energy loss rate criterion, signifying a decrease in the irreversibility of heat transfer between the high-temperature, high-pressure gas within the compression chamber and the cooling water. These findings provide a theoretical basis for optimizing the thermodynamic performance and cooling strategies of transcritical CO2 refrigeration systems.