In the recent years, as a passive cooling method, night ventilation is getting more and more attention. To investigate the effectiveness of night ventilation under different climatic conditions in China, Beijing、Shanghai and Guangzhou were selected as the representatives of cold region、hot-summer and cold-winter region and hot-summer and warm-winter region respectively. The building energy simulation tool Energyplus was used to model an office building and calculate the cooling energy and total energy consumption of the building with and without night ventilation in the three cities. The energy-saving effect of night ventilation was analyzed by comparison. The results show that in the same month, the effectiveness of night ventilation is improved as the latitude is increased. For the whole cooling period, even if in hot-summer and warm-winter region, night ventilation can achieve distinct energy-saving effect.