this paper suggested a model to address two important but unexplored questions-how EPC affects the buildings energy-saving performance and how institutional legitimacy of ESCOs moderates the relationship between EPC and buildings energy-saving performance.The results indicate that the implementation of EPC has a positive effect on building senergy-saving performance.And also,the sociopolitical legitimacy positively moderates the relationship between the implement of EPC and buildings energy-saving performance and the cognitive legitimacy positively moderates the relationship between the implement of EPC and buildings energy-saving performance.