Abstract: High-salinity ion erosion and cyclic wet-dry alternation are major factors contributing to the seepage instability of artificial dams in underground pumped storage systems. Taking the underground reservoir of a coal mine in western China as the engineering background, the multi-scale damage evolution of concrete under a high-salinity mine water environment is investigated. A comprehensive approach combining field sampling of mine water, uniaxial loading CT scanning, microstructural analysis, and multi-field coupled numerical simulation was employed to examine the compressive strength attenuation, pore-crack evolution, and permeability variation of concrete under different immersion solutions and wet-dry cycles. A stress-seepage-damage coupling model incorporating the chemical effects of saline ions was developed to quantitatively describe the influence of wet-dry cycles and hydraulic pressure on the seepage range and damage evolution of concrete. Results show that high-salinity mine water significantly accelerates the deterioration of concrete during wet-dry cycling. The inflection point of compressive strength attenuation shifts from 20 cycles in the control group to 10 cycles under saline conditions, and the strength decreases by 51% after 30 cycles (compared with 27% in the control group), indicating pronounced early-stage damage sensitivity in saline environments. The rate of porosity change reaches its peak at 10 cycles and evolves synchronously with the strength decay, reflecting a feedback mechanism between pore-crack development and mechanical degradation. The numerical results of the stress-seepage-damage coupling model agree well with the experimental data in terms of stress-strain evolution, peak strength, and porosity variation, with key mechanical parameter errors below 5%, confirming the model’s reliability. The seepage response indicates a nonlinear increase in penetration distance with increasing wet-dry cycles and hydraulic pressure, which tends to stabilize after 10 cycles as the crack network approaches saturation. Within the hydraulic pressure range of 0.8−1.2 MPa, the seepage distance shows the highest sensitivity, revealing a critical effect of pressure-driven pore activation. Microstructural analyses further demonstrate that the synergistic corrosion of Cl⁻, \mathrmSO_4^2- , and Mg²⁺ ions induces ettringite formation, C−S−H gel decomposition, and localized crystal expansion, producing a staged damage mode characterized by “compaction-expansion-permeation”. This process is accelerated by alternating wetting and drying, leading to gradual crack coalescence and a substantial increase in permeability. The study elucidates the multi-scale damage mechanism of concrete under high-salinity mine water, covering macroscopic strength degradation, mesoscopic pore-crack evolution, and microscopic chemical deterioration. It provides a theoretical basis and engineering reference for durability evaluation and protection design of artificial dams in underground pumped storage systems.