[Objective] In order to solve the problems of strong permeability, weak water retention capacity of the coarse-grained slag, and serious leakage of the slope surface of the coarse-grained slag, the improvement effect of reducing leakage using modified hydrophilic polyurethane resin binder (W-OH) solution with different concentrations on the slope of gravel slag was investigated. [Method] Focused on a highway slag slope in the rocky desertification area of Guangxi Zhuang Autonomous Region, artificial erosion experiments were conducted on the gravel slope surface added W-OH solution with different concentrations using different erosion flow rates at the slope site. [Results] The study found that untreated slope experienced severe leakage, for which the runoff on the slope only appeared when the scouring discharge was greater than 30 L/min. When the scouring discharge was 30 L/min, the runoff rate accounts for just 18.3% of the incoming flow rate, and 81.7% of water was lost due to slope leakage. However, The average runoff rate and average infiltration rate of the slope after treatment with W-OH solution increase with the increase in the inflow rate and W-OH solution concentration. The stable runoff rate of the slope treated with W-OH solution with a concentration of 3% to 6% increases by 200% to 385.5% compared to that of untreated slopes, and the higher the concentration of W-OH solution, the better the treatment effect on the slope. The infiltration runoff ratio decreases with the increase in inflow rate and W-OH solution concentration. [Conclusion] After treatment with W-OH solution, the leakage of coarse-grained slag-slopes was effectively reduced, so that the water retention capacity of the slope was improved and it was contributed to slope vegetation restoration.