Objective: This study aimed to investigate the effect of internal heat exchanger on the performance of transcritical CO₂ two-stage compression/ejector refrigeration system. Methods: The simulation software was used to analyze the effects of the internal heat exchanger on the suction temperature, discharge temperature, specific work increment of the low-pressure compressor and system performance coefficient under different gas cooler outlet temperatures (25～45 ℃), high-pressure side discharge pressure (7.4～9.5 MPa), evaporation temperature (-40～-15 ℃) and intermediate pressure (3～5 MPa). Results: With the increase of intermediate pressure, the discharge temperature and specific work increment of the low-pressure compressor increased at a specific regenerative degree. However, with the increase in evaporation temperature, the discharge temperature and specific work increment of the low-pressure compressor gradually decrease. Under the control of this standard conditions, the coefficient of performance of the regenerative system is lower than that of the system without regenerative, and the energy efficiency of the regenerative system decreases with the increase of the regenerative degree. Conclusion: The suction temperature, discharge temperature, and specific work increment of the low-pressure compressor all rise significantly as the internal heat exchanger increases. However, the internal heat exchanger does not improve the performance of transcritical CO₂ two-stage compression/ejector refrigeration system.