Abstract: This paper takes a highfill slope in Anning in Yunnan Province as a case, using investigation, monitoring and other methods, on the basis of the distribution characteristics of red clay, the physical and mechanical properties of red clay before and after filling were analyzed, then the stability of slope was studied by numerical simulation software. The results show that the physical and mechanical indexes of the red clay foundation decrease first and then increase before and after the fill project, the stability of the fill slope shows the trend of decrease first and then increase. The ground fissures in the upper part of the slope resulted from the uneven deformation of the slope body were caused by the filling body and the foundation soil consolidation under the unfavorable combination of the foundation soil of the original topography and the uneven thickness of the filling soil, and the slope body is stable in general. Research result has certain reference value and guiding significance to the highfill slope project design of red clay foundation, the study on the influence to slope stability by physical and mechanical index of red clay foundation, the control of inhomogeneous deformation during the construction, crack hazard in the upper part of slope.