<p>The stability and reliability of compressed air energy storage (CAES) caverns depend on the rock mechanical performance and durability of sealing layer. This study investigates the suitability of butyl rubber as a sealing layer for CAES caverns. Mechanical property tests, such as high–low temperature cycling tests and fatigue damage tests, were conducted to analyze the evolution of mechanical properties and micro-damage in butyl rubber under high–low temperature cycling environment. Based on the test results, fatigue damage equations of butyl rubber were established at different strain levels. Additionally, a numerical model developed in FLAC3D was used to simulate the stress and deformation responses of the sealing layer under undamaged, pressure-damaged, and thermo-mechanical coupled damage conditions. The results indicate that butyl rubber exhibits excellent tensile properties, but its shrinkage performance decreases after high–low temperature cycling. After 400 temperature cycles, the ultimate tensile strength and ultimate tensile strain decreased by 41.55 and 87.31%, respectively, compared to uncycled specimens. After 100 charging and discharging cycles of operation of the cavern, the maximum hoop tensile strain in the sealing layer was 0.998%, far below the material’s ultimate tensile strain. This means that the butyl rubber layer could effectively prevent structural failure and leakage due to tensile damage. However, under long-term CAES operating conditions, the coupled effects of temperature and pressure gradually degrade the deformation capacity of the butyl rubber, which leads to the risk of tensile failure in the butyl rubber sealing layer.</p>