Data centre grows rapidly all over the world, at the same time energy consumption is also increasing. According to research, nearly 45% of the total energy in data centre is used for IT equipment while about 45% for computer room air conditioning (CRAC) system. Apparently, cooling system consumes too much energy. Badly air organization and compressor of air conditioning working all year round are the mainly two shortcomings for CRAC system. In order to save energy, a new kind of cooling system called separated heat pipe cooling system is used in data centre. This system has better airflow organization and it can use free cold ambient air as heat sink in winter. In this paper, working condition of separated heat pipe system is tested. For example, temperature at some typical points will be measured, like chilled water’s inlet/outlet temperature; IT equipment’s working temperature and room temperature. On dealing with temperature distribution, T-Q diagrams of CRAC and separated heat pipe system showing the temperature distribution are drawn. In T-Q diagram, temperature difference of heat transfer in every process can be easily calculated, which can be used to direct heat transfer enhancement. As for an evaluation index of data centre energy efficiency, PUE (power usage efficiency) will also be measured. In theory, the system’s PUE will get the minimum value in winter, while get the maximum value in summer. Briefly, using free ambient cold air and installing evaporator inside the rack are the mainly two advantages of separated heat pipe system, which will lead to better working environment for IT equipment and more energy saving compared with traditional CRAC system.