<p>The deterioration of deep roadway sandstone ore pillars (cores) under cyclic dry–wet conditions was investigated through an integrated approach. The MTS-815 rock mechanics experimental system, scanning electron microscopy, nuclear magnetic resonance testing, and X-ray diffraction analysis were employed to examine the evolution of the mineral composition, microstructure, and pore structure of the sandstone during the dry–wet erosion process under varying relative humidity environments. This multi-scale analysis elucidated the deterioration mechanisms affecting the macroscopic mechanical properties of the sandstone. The study reveals that: (1) increased dry–wet cycles under environmental humidity weaken the intergranular bonding of dense mineral structures, leading to feldspar decomposition, pore structure loosening, and a rise in exfoliated particles; (2) with higher environmental humidity and more dry–wet cycles, sandstone experiences a "damage–linkage–invasion" effect from the periphery to the center, resulting in reduced peak deviatoric stress, elastic modulus, and increased Poisson's ratio, exacerbating sandstone deformation and instability; (3) as dry–wet cycles increase, medium and small pores evolve into larger ones, and the expansion of these pores generates pressure that enlarges small pores, a phenomenon intensified by higher humidity; (4) the mineral content reduction rate, <i>η</i>_m, quantifies mineral depletion during dry–wet cycles, showing that sandstone deterioration correlates with calcite and feldspar depletion. The findings of this investigation can enhance the safety considerations during the excavation of deep underground roadways, and offer crucial theoretical foundations for the prospective assessment of preserved ore pillars and the stability of the surrounding rock mass.</p>