Natural-gas-driven building cooling heating and power (BCHP) system shows high energy efficiency and low greenhouse gases emission, but is of dissatisfactory performance under part load working conditions due to the non-synchronized and fluctuating thermal and electrical demands. Integrating thermal energy storage (TES) device with BCHP system proves to be an effective way to improve the performance of the whole system. In this paper, the applicability of TES-BCHP system is investigated according to the relationship between user load demands and system energy supply. Based on the supply thermal power ratio of the prime mover and the required one of users, a new parameter, the degree of mismatch (DM), is defined. Moreover, the analytical relationship between primary energy saving ratio (PESR) of TES-BCHP system and DM is established, under following thermal load (FTL) and following electrical load (FEL) respectively for three typical working conditions. The results show that the more DM approaches to unity, the higher PESR of TES-BCHP will be, and that the exportability of the co-generated electricity is favorable for energy saving. It also indicates that TES-BCHP is more applicable for those where the heating demand is dominant. This work is of great significance in further understanding the energy saving mechanism between TES and BCHP and guiding the design of practical TES-BCHP systems. (C) 2016 Elsevier Ltd. All rights reserved.