Abstract: Firstly, considering the different energy levels of multiple energies, the regional integrated energy system（RIES） is divided into five links: energy supply, energy conversion, energy transmission, energy storage and energy demand. Also, an expression of energy utilization efficiency（EUE） for evaluating RIES is proposed. Secondly, through the theoretical analysis on related factors of EUE, it points that penetration of renewable energy, efficiency of energy conversion equipment and capacity allocation structure, demand structure of cool/heat/electricity load in five parts of RIES are the core elements, which affect the EUE of RIES. Finally, a case study of a certain demonstration district in China is given to show that the energy efficiency expression can accurately reflect the characteristics of multi-energy complementary coupling and cascade utilization of RIES. By analyzing the EUE of RIES, the importance and method of reasonably allocating energy conversion equipments and optimizing the demand structure of cool/heat/electricity load are demonstrated, which is consistent with the theoretical analysis. The validity of the proposed EUE of RIES is illustrated.