Abstract: High filling slopes are widely used in airports and water conservancy projects in mountainous areas. Excavating steps at the interface of bedrock and soil filling can improve slope stability. Using Bishop's and finite element methods, the contribution of excavation steps on foundation-filling interfaces to improve the stability of a high fill slope is studied. Taking a high filling project in a southwest mountainous area as an example, the influence of excavation steps on slope stability is analyzed with the consideration of a heavy rain and an earthquake situation. Step excavation cannot significantly improve slope stability. The shape of steps and the relative strength of foundation-filling interfaces should be considered. When the strength of bedrock is high and the interfacial folding coefficient is small, step excavation is beneficial to improve stability. The higher the relative strength is, the smaller the effect of steps is. On the contrary, the closer the interface reduction coefficient is to 1, the weaker the step effect is. When the steps are located at the foot of a slope, it is beneficial to increase the stability of the slope. The influence of excavation steps on stability is unaltered.