To analyze the evaluation of the optimal discharge pressure in subcooler-based transcritical CO2 system, a prototype was tested under various working conditions. Experimental data showed that the power consumption increased while the heating capacity increased first and then kept unchanged even decreased with CO2 discharge pressure increased. Thus, COP increased first and then decreased, which verified the existence of the optimal discharge pressure in the subcooler-based system. The water temperature in CO2 gas-cooler exit rose obviously while that in R134a condenser exit reduced with discharge pressure increased. Besides, the optimal discharge pressure decreased with the decline in air temperature, water return temperature and water delivery temperature among the testing range. Comparing with the optimal discharge pressure in the single used transcritical CO2 system, the optimal value in the subcooler-based system was much higher, and the difference between the two pressures decreased with the air temperature decreased. (C) 2017 Elsevier B.V. All rights reserved.