Abstract: There is a passive containment cooling system (PCCS) in the AP / CAP series nuclear power plants, to cool the containment  passively within 72 hours after accidents. However, after 72 hours, if the top tank is not able to replenish water in time, it is difficult to take all the residual heat away by the containment itself, and there exists potential overpressure for the containment. To solve the problem of the time limit in the residual heat removal of the containment in nuclear power plants, an experiment system for an innovative passive residual heat removal system for the containment is built,  to study the heat transfer performance under different pressure, temperature and gas composition under design basis accident (DBA) conditions. The results show that the heat capacity of the system completely meets the design. Further, the correlation formula of the external tube condensation heat transfer coefficient with non-condensable gas for low subcooling condition is given.