<p>Acid rain poses a threat to the stability of open-pit coal mine slopes, which are often composed of coal-rock combinations. Hence, we explore the damage and degradation mechanisms of such combinations under acidic dry–wet cycles. Uniaxial compression and acoustic emission tests were performed on coal-rock specimens exposed to different acidic conditions (pH = 7, 5, and 3) and varying numbers of dry–wet cycles (<i>n</i> = 0, 5, 10, 15, and 20). Pore size, mineral composition, and strain characteristics were observed using scanning electron microscopy, nuclear magnetic resonance, and X-ray diffraction analysis. The results indicate that under acidic dry–wet cycles, the compressive strength and elastic modulus of the coal-rock combination decline with increasing cycle numbers, most significantly at pH = 3, followed by pH = 5 and pH = 7. The increase in cycle numbers and decrease in pH value affect microcrack development and failure modes, including axial tensile splitting, single-plane and multi-plane shear failure, and buckling and spalling failure. Significant differences exist between coal and sandstone under dry–wet cycles. The sandstone section sustains more severe damage, with more pronounced changes in pore structure and mineral composition, leading to a greater reduction in mechanical properties compared to the coal section. Sandstone is more prone to shear and spalling failure, while coal is more likely to experience tensile failure. Our findings offer scientific and theoretical bases for analyzing the stability of open-pit coal mine slopes in acidic rainy regions. The most severe degradation occurs during the first five cycles, underscoring the necessity of early intervention and continuous monitoring in such environments.</p>