Abstract: Riparian vegetation plays a vital role in maintaining multiple ecosystem functions and providing various ecosystem services for human society. Especially, riparian vegetation acts as a buffer for the stream by intercepting and retaining sediment, nutrients, and pollutants carried in surface runoff before they enter the stream. However, the buffering effects of riparian vegetation are sometimes limited by different factors, such as soil type, slope gradient, rainfall and scouring intensities, and vegetation coverage. Therefore, the upstream of the Beijiang River in Guangdong Province of southern China was selected as a case, and the characteristics of riparian vegetation in inhibiting runoff and sediment in erosion process of red soil slope were explored in this paper. Specifically, using the runoff scouring experiments in situ, the characteristics of riparian vegetation in inhibiting slope erosion along Beijiang River were explored, which aimed to further clarify the effects of riparian vegetation on relationship between overland flow and sediment yield as well as the response of inhibiting effect of vegetation to slope gradient and scouring intensity. The results show that the time of runoff initiation and duration of runoff recession on riparian slope along the Beijiang River exhibited obvious rule under the condition of runoff scouring, namely, the existence of vegetation can delay the time of runoff initiation under the same condition of slope gradient and scouring intensity, and the greater slope gradient and scouring intensity can result in the earlier runoff generation. Vegetation can reduce the runoff coefficient of riparian slope, while the trapping effects of riparian vegetation on runoff amount can be decreased in spite of the fact that the runoff coefficient increases with the increasing slope gradient and scouring intensity. The inhibiting effect of vegetation to slope runoff is more significant under lower slope gradient and scouring intensity. The inhibiting effect of vegetation to runoff coefficient at different slope gradients is 3.35%, 3.36%, 4.28%, and 3.17%, respectively, while under different scouring intensities it is 21.69%, 17.40%, and 10.01%, respectively. Riparian vegetation can reduce runoff erosivity in slope soil erosion process, and greater slope gradient and scouring intensity can result in lower inhibiting effect of vegetation to runoff erosivity. The inhibiting effect of vegetation to runoff erosivity at different slope gradients is 60.00%, 32.23%, 27.29%, and 22.76%, respectively. Riparian vegetation can effectively improve the resistance ability of soil and reduce the yield and median particle size of sediment. The effect of vegetation in inhibiting sediment, which is 60.14%, 32.83%, 24.19%, and 20.86% respectively, is larger than that in inhibiting runoff. Correlation analysis showed that the time of runoff initiation is significantly and negatively correlated with accumulation of sediment yield and sediment particle size, and vegetation can alter relationship between the duration of runoff recession and accumulation of sediment yield and sediment particle size. Runoff coefficient and runoff erosivity both are significantly and positively correlated with the accumulation of sediment yield and sediment particle size, and the effect of vegetation in inhibiting the accumulation of sediment yield and runoff erosivity reduces with the increasing slope gradient and scouring intensity. In conclusion, effect of riparian vegetation in inhibiting erosion sediment is larger than that in inhibiting slope runoff, and is significantly influenced by slope gradient and scouring intensity. Results from the present study can provide the basis for watershed soil and water conservation as well as the restoration and reestablishment of riparian vegetation.