Abstract: To clarify the mechanical destabilization and fracturing characteristics of deep limestone subjected to high-confining-pressure unloading, a series of triaxial tests with synchronous acoustic-emission (AE) monitoring was performed on standard limestone cores. Specimens were first loaded to 80% of their triaxial compressive strength under initial confining pressures of 40, 50, and 60 MPa; then, the confining pressure was reduced at a constant axial load, with unloading rates of 0.05, 0.10, 0.20, 0.30, and 0.40 MPa·s⁻¹, while continuously recording AE signals. The coupling effect of the initial confining pressure and unloading rate on strength degradation, AE response, and failure-mode transition was systematically investigated. The experimental results showed that the unloading rate and initial confining pressure significantly affected the mechanical behavior and failure mode of limestone. Under constant confining-pressure conditions, the peak deviatoric stress was significantly negatively correlated with the unloading rate. The strain development pattern is controlled by the unloading rate of the confining pressure, and its critical threshold increases with the rise in confining pressure. When the unloading rate is below the threshold, strain stagnation occurs; otherwise, the deformation transitions to continuous strain development. The strengthening effect of the confining pressure was rate dependent—increasing the confining pressure enhanced the shear strength of the rock samples, whereas it reduced both the sensitivity of the samples to the unloading rate and the differences in the limestone strength associated with different unloading rates. The ringing count and amplitude distribution of AE in the limestone revealed its damage evolution. Under confining pressures of 40 and 50 MPa, the activity in the later stage of failure was intense, the cumulative curve rose sharply, and the stress crack response was synchronous. Under a confining pressure of 60 MPa, a sudden change in the cracks was observed in the early and middle stages, with a stepwise increment in the curve and a characteristic of “stress accumulation delayed fracture.” The amplitude signal indicated that as the unloading rate increased, cracks developed dynamically from a single-point explosion to global expansion. Evidently, the higher the initial confining pressure, the more energy is stored inside the rock mass, and crack development and expansion occur more frequently during the unloading of the confining pressure, resulting in a fluctuating b-value curve. As the unloading rate of the confining pressure increases, stress release intensifies, and the crack dynamics transition from steady-state propagation to abrupt penetration. The overall b-value curve drops and is accompanied by high-frequency fluctuations. Under the combined effect of these two phenomena, the b-value of AE in the limestone evolves from gentle to jumping, and the release of energy and micro-fracture activity are significantly enhanced, indicating an increased risk of instability and failure. The evolution of failure modes is jointly controlled by the confining pressure and loading rate. Increasing the confining pressure suppresses tensile failure and enhances shear action; at low rates (0.05 MPa·s⁻¹), failure is mainly due to shear, whereas at high rates (0.40 MPa·s⁻¹), tensile failure occurs. The critical rate (0.10–0.30 MPa·s⁻¹) represents the transition zone for the change in failure modes.