<p>Whether and how environmental regulation affects ecological security remains a subject of academic debate, particularly concerning the largely unexplored contingent role of energy ecological efficiency (EEE). This study addresses two primary research questions: (1) How significantly does environmental regulation impact regional ecological security, and through what mechanism does this relationship operate? (2) How does energy ecological efficiency (EEE) precisely moderate this relationship? Utilizing panel data from 13 prefecture-level cities in Jiangsu Province, China (2008–2020), we evaluate ecological environment quality (EQ) and ecological security (ES) using a hybrid approach of TOPSIS, AHP, and grey relational analysis. EEE is evaluated via a super-SBM DEA model, and empirical testing is conducted using a two-way fixed-effects model. The results demonstrate that while environmental regulation contributes positively to ecological security, this effect is primarily indirect, transmitted through significant improvements in ecological environment quality. Furthermore, EEE serves as a positive moderator between environmental regulation and EQ, suggesting that regulatory efficacy is dependent upon the level of regional energy–economic–ecological coordination. These findings, which remain robust across multiple sensitivity tests and endogeneity checks, clarify the internal mechanisms linking regulation to security. The identification of EEE as a critical enabling factor provides significant policy implications for regions seeking to coordinate export-led growth with ecological sustainability.</p> Graphical abstract <p></p>