AbstractFree cooling is one of the most potential ways of reducing the energy consumption of data centers. Thermosyphon has superior heat transferability thus it is suitable for application in free cooling. However, a separate thermosyphon free cooling system usually cannot provide sufficient cooling capacity in warm seasons. In order to overcome this weakness and avoid two sets of equipment, hybrid system of thermosyphon free cooling and vapor compression refrigeration for data centers has been developed by researchers. The cooling performance of this kind of system depends greatly on the climate outside therefore its applicability in different time and zones needs to be studied. In this paper, the climate data from five cities of different climate zones in China is collected. The performance model of the hybrid system is built up. Based on the climate data and performance model, the annual energy consumption is then calculated and compared with traditional air conditioner. The result shows that the energy-saving potential of the hybrid system varies in different climate zones, and when the mode switching temperature is relatively high, it is distinct in most climate zones of China.