Abstract: Passive containment cooling system (PCCS) is an important engineered safety feature in generation Ⅲ advanced pressurized water reactor. A PCCS using separated heat pipe technology was promoted. Flow and heat transfer characteristics during the system start-up and in steady state were studied by mechanism test and systematic thermal hydraulic analysis code. Key influencing factors on operation and heat removal capacity of the system were also discussed and feasibility of the system design was validated. The results show that the heat removal capacity of the system has strong self adaptability with containment conditions. The system is a feasible and effective approach to passively cool the containment in accident conditions. Comparisons between code analyses and the test and existing research results show that RELAP5 code is an applicable thermal-hydraulic analysis code for the system. Key flow and heat transfer parameters change in the vaporization heat transfer tube, such as flow regimes, heat transfer modes and void fractions, indicates that heat removal capacity of the system is significantly affected by initial fluid filling rate. Minor height difference between cold and hot cores is able to provide sufficient natural circulation driven force, and that is not an important restriction factor for the system arrangement.