Aims <p>This study investigated the impact of coal gangue-reconstructed soils on water dynamics and alfalfa growth in the degraded arid Jungar mining area of Inner Mongolia. The objectives were to quantify soil water variations under different amendment ratios and layer thicknesses, evaluate their effects on alfalfa growth, and elucidate the underlying mechanisms for optimized ecological restoration.</p> Methods <p>Controlled indoor soil column experiments simulated different coal gangue:topsoil volume ratios (1:2, 1:1, 2:1) and reconstructed layer thicknesses (40–60&#xa0;cm). Soil water content was measured spatially and temporally, and alfalfa growth indices were assessed.</p> Results <p>The addition of coal gangue significantly influenced soil water stability and distribution. Lower coal gangue proportions (1:2 ratio, Group B) and topsoil (Group D) demonstrated superior water retention capacity. In contrast, higher coal gangue proportions (2:1 ratio, Group C) resulted in enhanced soil moisture stability and improved profile uniformity across depths. However, the incorporation of coal gangue generally inhibited plant growth, with the most significant negative impact observed on alfalfa germination rate. Correlation analysis revealed that in amended soil groups, a relationship exists between excessive surface moisture, potentially stemming from reduced soil aeration, and suppressed alfalfa growth.</p> Conclusion <p>Coal gangue amendment presents a potentially economical solution for land reclamation in semi-arid mining areas by improving soil hydrology. The 2:1 ratio (Group C) significantly enhances moisture stability and reduces topsoil dependence, offering cost-effectiveness. However, the observed growth suppression, potentially a consequence of poor soil aeration, necessitates balanced strategies to optimize both economic viability and plant establishment for sustainable restoration.</p>