Abstract: As an innovative energy technology that deeply integrates CO₂ geological sequestration with compressed gas energy storage, compressed CO₂ storage in saline aquifer achieves dual benefits by using CO₂ as a circulating working fluid, simultaneously enabling large-scale carbon sequestration and grid-level energy storage. This technology aligns well with China's strategic development needs for energy transition and the “dual carbon” goals, offering broad application prospects. However, current research on compressed CO₂ energy storage in saline aquifer primarily focuses on optimizing ground systems, with limited attention given to the underground factors that ultimately determine the success or failure of the entire project. Therefore, this paper reviews the key geomechanical issues related to compressed CO₂ energy storage in saline aquifer. First, it summarizes state of the art in compressed gas energy storage technologies worldwide, and introduces the basic principles and operational characteristics of compressed CO₂ energy storage in saline aquifer systems. Second, it summarizes the thermodynamic properties of CO₂, highlighting the advantages of CO₂ as a working fluid compared to air. Third, it addresses key geomechanical challenges facing geological storage systems, detailing the multiphase coupling mechanisms between CO₂, brine, and rock during system construction and operation. It examines the potential stability and integrity issues arising from these interactions, including formation and surface deformation, sand production, caprock fatigue and fracturing, fault reactivation and induced seismicity, sealing mechanisms of caprock/faults, and leakage pathways. Finally, it summarizes the shortcomings and challenges in current research on compressed CO₂ energy storage in saline aquifer and proposes several research recommendations.

Key words: saline aquifer, compressed CO₂ energy storage, geomechanics, stability, sealing