Abstract: In order to studied the water conservation function of litter layer and soil layer of oak forest in Haikou State Forest Farm, and provide theoretical basis for the construction of water conservation vegetation and comprehensive management of water resources in this area. We set up 9 typical plots in oak forest of the study area. The hydrological effects of litter and soil layers were studied by the methods of plot survey, ring knife, drying and soaking. The results showed that the indexes of litter layer and soil layer were different in different oak stands, and the range of effective interception of litter layer was 9.39–10.25 t/hm², and the effective interception of soil layer was 323.60–440.60 t/hm². The largest comprehensive water storage capacity of the 3 stands is 449.99 t/hm² of Cyclobalanopsis glaucoides mixed forest, followed by 415.92 t/hm² of Lithocarpus dealbatus mixed forest, and the smallest is 333.85 t/hm² of Quercus franchetii Skan mixed forest. soil is the main body of water conservation function, but litter also plays an important role in slowing down surface runoff and improving soil structure.