Abstract: BackgroundIn rocky mountain areas, the soil layer is thin and poor in water retention capacity. Soil moisture condition is a crucial factor restricting vegetation growth and ecosystem stability. Methods Based on the environmentally friendly PVA-CS/SA-Ca²⁺ hydrogel developed in the previous stage, this study adopted the method of simulated artificial rainfall experiment to explore the mechanism of the hydrogel on soil moisture preservation and supplementation by investigating the slope runoff generation process, soil water content, and water retention capacity.Results The hydrogel could alter the characteristics of slope runoff: under rainfall intensities of 30 mm/h, 60 mm/h, and 90 mm/h, it delayed the initial runoff generation time by 37.4%, 32.5%, and 21.7%, respectively, and reduced the total runoff volume by 7.6%, 5.9%, and 5.7%, respectively. Additionally, the hydrogel could increase soil water content over a long time scale. Under different rainfall intensities, the soil water content increased by 12.8%, 7.6%, and 3% at the end of the rainfall process, and the reduction of soil moisture was decreased by 23.1%, 22.9%, and 35.3% after 7 days. Conclusion The hydrogel developed in this study can effectively play a role in moisture preservation and soil water supplementation, providing technical support and a theoretical basis for dry and barren sites where moisture is the main limiting factor.