The gap between the designed and actual energy performance of buildings (BEPG) poses a severe challenge to achieving building energy efficiency goals and has garnered global attention. However, previous studies have predominantly concentrated on the identification of factors influencing BEPG and have not systematically explored the interrelationships among these factors. In this study, the Integrated Decision-Making combined with Trial Evaluation Laboratory and Adversarial Interpretive Structural Modeling (DEMATEL-AISM) were employed to explore the driving mechanism for BEPG. Initially, a total of 40 influencing factors were identified through literature review and interviews, and 18 representative factors were selected from the building lifecycle perspective. Subsequently, the importance level and causal attributes of each influential factor were assessed by the DEMATEL method. Furthermore, a multi-level hierarchy was constructed based on the AISM model to illustrate the intricate interrelationships among the representative factors. The results indicated that there were seven cause factors and eleven effect factors for BEPG, with the six most significant factors were setting errors in simulation, lack of supervision, performance of equipment, differences in building performance, occupant behavior, and improper design. Additionally, the hierarchical structure model was categorized into five levels, which comprehensively indicated the driving relationship between the 18 influencing factors and the generation mechanism of BEPG. Finally, nine targeted strategies to address BEPG were proposed. This study offers new insights into the mechanisms of BEPG formation through the integration of DEMATEL and AISM, providing a robust framework for researchers and practitioners to systematically understand and address BEPG, as well as essential guidance for policymakers to develop effective strategies to reduce BEPG.