In this paper, application potential of phase change heat storage coupled with night ventilation technology in transition and hot seasons were investigated using EnergyPlus, based on a typical office building in Xi'an. Two factors, daily cumulative cooling amplitude (ΔT) and percentage of cooling potential (J), were introduced to evaluate its cooling effect. The characteristics of outdoor dry-bulb temperature were examined when the technology realized its best cooling potential. The performance of the technology on improving the indoor thermal environment was also analyzed based on the standard ASHRAE 55 Adaptive Comfort Model. The results indicate that the technology can obtain excellent application effect when the maximum of outdoor dry-bulb temperature exceeds the upper limit of the phase change range 3℃ and its minimum is less than the lower limit of the phase change range 3℃ and its average is in the phase change range. The application effect of this technology in transition season is superior to that in hot season. Compared with night natural ventilation technology, the cooling amplitude in transition season and hot season by using the technology are increased by 14% and 5.6%, respectively, and the number of hours meets ASHRAE 55 standard 80% acceptability limit in transition and hot seasons are increased by 8% and 1%, respectively.