Abstract: The classical Green-Ampt model assumes that the wetting zone is completely saturated when analyzing the rainfall infiltration law of the shallow slope, without considering the infiltration transition zone and its influence on the permeability coefficient of the soil. In order to explore the rainfall infiltration law of slope and study the change of soil permeability coefficient with the rainfall process, the theoretical model of the water profile of slope is established based on considering the infiltration transition zone. According to the proportion of the thickness of the transition zone in the wetting zone, the actual permeability coefficient of the soil in the wetting zone was modified based on the unsaturated permeability characteristics of the soil and the Van Genuthen model. Based on this, an improved Green-Ampt infiltration model was established. Compared with the calculation results of the Richards equation and the existing test results, the theoretical model in this paper can accurately reflect the variation of slope infiltration rate and wetting front depth with rainfall time, and the accuracy is higher than that of the classical Green-Ampt model, which can verify the accuracy of the model in this paper. The influencing factors of slope seepage law are further discussed and analyzed. The results show that the infiltration rate of soil and the wetting front depth is controlled by rainfall intensity. The larger the rainfall intensity is, the faster the wetting front advances and the earlier the runoff appears on the slope surface. Different soil types have different permeability characteristics, which directly affect the infiltration law of soil. In general, the wetting peak of coarse-grained soil slope is the fastest, followed by clay loam, and silty clay loam is the slowest. The higher the initial water content of the hill, the greater the wetting peak depth of the slope under the same total infiltration.