To analyze the effect of summer ventilation on the thermal performance and energy efficiency of buildings utilizing phase change materials (PCMs), this paper simulated the indoor temperature variation and energy saving performance of buildings constructed with PCM under different ventilation conditions from June to September. With EnergyPlus and degree-day method, 48 ventilation schemes, including eight ventilation periods (3 h per period) and six ventilation quantities (0.5 ac/h to 3 ac/h), were modeled and simulated in five cities located in different climate regions in China. According to the results, it is believed that the simultaneous use of PCM and ventilation can significantly improve the indoor thermal comfort and offer a good energy saving performance in summer. Considering the economic benefits, different optimal ventilation schemes (including ventilation periods and ventilation quantities) were suggested for different climate regions.