Abstract: Coal gangue is a waste material produced during the coal mining process and can also serve as a raw material for the improvement of desertified soil. We investigated the impact of coal gangue with different particle sizes (<2 mm, <1 mm, <0.5 mm) and proportions (1∶1, 2∶1, 1∶2) on the amelioration of desertified soil by examining water characteristics such as infiltration and evaporation, aiming at determining the particle size and blending ratio of high-quality coal gangue. The results showed that the addition of coal gangue changed the texture of the mixed soil from sandy to sandy loam. As the particle size of coal gangue decreased, the water infiltration rate decreased, while the total porosity, saturated water content, field capacity, and cumulative evaporation volume increased. However, when the particle size of coal gangue was constant, the infiltration rate increased and the cumulative evaporation decreased with the increase of coal gangue content. The Kostiakov infiltration model was found to be more suitable as the infiltration model for the mixed soil. The results of the two-factor analysis indicated that the particle size of coal gangue had a more significant impact on water characteristic values such as total porosity, saturated water content, and field capacity, while the coal gangue-soil ratio had a more significant influence on water infiltration and evaporation than particle size. This study provides substantial theoretical support for the improvement of desertified soil along the middle reaches of the Yellow River Basin, and provides a reference for the rational utilization of coal gangue, which is expected to reduce the improvement cost and improve the restoration effect.