[Objective] The influencing mechanisms of synergistic improvement by biochar and potassium polyacrylate on the water characteristics of coal gangue in alpine mining areas were investigated， in order to enhance its water-holding and moisture conservation capacity and inhibit water loss via evaporation. [Methods] A laboratory soil column simulation experiment was conducted with different mass fractions of biochar （1.1%， 4.3%） and potassium polyacrylate （0.12%， 0.22%， 0.32%） in combined application （six treatments in total）， along with a control （CK）. The one-dimensional constant-head vertical infiltration method， continuous weighing method， and cutting-ring method were employed to determine the infiltration characteristics， evaporation process， and key water-holding parameters （saturated water content， capillary water-holding capacity， and field capacity） of the coal gangue matrix. [Results] The saturated water content of all treatments increased by 7.88% to 33.35% compared with CK. The addition of potassium polyacrylate significantly inhibited the transport distance of the wetting front， initial infiltration rate， average infiltration rate， and cumulative infiltration volume （p<0.01）. The multi-level pore adsorption of biochar， combined with the swelling and resistance-enhancing effect of potassium polyacrylate， jointly formed a ‘slow infiltration-strong water retention’ mode. This mode effectively inhibited rapid water infiltration and enhanced the capture and storage efficiency of water （e.g.， freeze-thaw water） in the root zone. The Kostiakov model could accurately characterize the infiltration patterns of the amended matrix （R²>0.916， RMSE<0.159）. Treatments with high amendment rates （e.g.， B₄P₃） showed significant evaporation inhibition effectiveness， achieving a maximum reduction of 19.88% in cumulative evaporation loss rate compared to CK， while maintaining higher residual water content. Under a bulk density of 1.41 g/cm³， considering water-holding characteristics， infiltration characteristics， and evaporation inhibition performance， the optimal amendment ratio of the coal gangue matrix was achieved in the B₄P₃treatment group， with a biochar mass fraction of 4.3% and a potassium polyacrylate mass fraction of 0.32%. [Conclusion] The B₄P₃ treatment significantly enhances the water-holding capacity and evaporation inhibition ability of coal gangue in alpine mining areas. The Kostiakov model demonstrates the best fit for the water infiltration process across all treatment groups.