Abstract: To investigate the mechanical behavior and failure mechanisms of limestone under high confining-pressure unloading conditions, high confining-pressure unloading tests combined with acoustic emission (AE) synchronous monitoring experiments were designed and conducted. The experiments utilized standard cylindrical limestone specimens, conducting conventional triaxial unloading tests at initial confining pressures of 40, 50, and 60 MPa, with unloading rates of 0.05, 0.1, 0.2, 0.3, and 0.4 MPa/s. Stress-strain curves and acoustic emission signals were synchronously collected. The study found that the unloading rate significantly affects the mechanical response and failure mode of limestone; at the same confining pressure, a higher unloading rate leads to a lower peak differential stress, and the failure exhibits more pronounced brittle characteristics. Conversely, at lower unloading rates, the rock demonstrates ductile failure, with delayed peak stress and more complete release of strain energy. An increase in confining pressure can suppress crack propagation and enhance shear strength; however, the sensitivity of the unloading rate's influence on strength diminishes as confining pressure increases. The results of the acoustic emission monitoring indicate that an accelerated unloading rate leads to a significant increase in ringing counts and cumulative ringing counts, with more intense acoustic emission activity. Furthermore, the damage evolution process under high confining pressures is more complex and prolonged; high-speed unloading is associated with frequent high-frequency and high-amplitude signals, indicating accelerated micro-crack expansion and penetration. The analysis of failure modes shows that the unloading rate and confining pressure jointly control the rock fracture mechanisms: at low rates, shear failure predominates, while high rates shift to tensile failure, and high-speed unloading under low confining pressure is prone to induce brittle fragmentation, whereas under high confining pressure, the main crack presents a serrated shear zone. The critical unloading rate serves as the threshold for the brittle-ductile transition, corresponding to a significant increase in the bifurcation of the cracks.