<p>In light of the constraints on explosives and the national "dual carbon" strategic goals, microwave-assisted impact rock breaking has emerged as a promising method for hard-rock roadway excavation due to its environmental benefits and efficient rock-breaking capabilities. However, the underlying mechanism of this method remains poorly understood. This study establishes a meso–macro-unified theory for microwave-assisted impact rock breaking by linking macro-level specific energy consumption attenuation to meso-level damage through strain energy density, based on thermodynamics and energy conservation principles. Using a self-designed dual-indenter impact test system (DHPB) and SEM, we investigated the variations in specific energy consumption and damage in limestone specimens under different microwave radiation durations. The results demonstrate that microwave radiation-induced degradation exhibits a threshold effect, heavily influenced by the initial crack length. When the strain energy density absorbed by the rock is below the threshold required for crack propagation, minimal internal damage occurs. Conversely, once the threshold is exceeded, damage accumulates nearly linearly with strain energy density. Experimental data show that the maximum specific energy consumption attenuation in limestone specimens reaches 0.58, accompanied by a damage increase of 0.59. These findings align with the meso–macro-unified theory, confirming that the increase in meso-level crack length and density quantitatively reduces macro-level specific energy consumption. This reveals the mechanism by which microwave radiation weakens rock resistance to impact. The study provides a theoretical foundation for the engineering application of microwave-assisted impact rock breaking in hard-rock environments.</p>