Soil erosion is a global environmental issue that can lead to the loss of nutrient-rich topsoil and even soil desertification, which is more severe in vulnerable and sensitive karst areas. Currently, it is imperative to explore the soil erosion mechanism and the weathering process to help prevent soil degradation in the karst area. In this study, we estimated the soil erosion rate of a representative karst slope in Shilin area of China by Cs-137 tracer method. We also analyzed the changes of soil total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) along the soil profiles. The results show that there is mild to moderate intensity erosion in this area, and erosion rates in different locations of slope are in the following order: hilltop > hillside > bottom. The Cs-137 content has a certain correlation with TOC, TN and TP content in the soil profile, which indicates they may have similar loss pathways. Furthermore, the chemical index of alteration (CIA), Na/K value and their relation with soil erosion are analyzed and reveal that the studied area is seriously affected by physical erosion and chemical weathering under a hot and humid environment area.