Abstract: This paper analyzes the engineering geological conditions and deformation failure characteristics of Xiangshuping landslide in Dejiang county, Guizhou. It establishes the evolved conceptual model of interbedded of soft and hard low-angle rock stratum that trends outside high slope. Its formation process can be summarized as the three stages of valley formation, namely：time-dependent deformation, sliding-stepwise cracking and sliding-bending-shear break. The instability mechanism and process of slope are reappeared through the numerical analysis of valley evolution and slope failure process. The effect of the interbedded of soft and hard layer on the slope evolution is quantitatively analyzed. The conclusion is that the limitation of the hard rock layer on the deformation of soft rock layer makes it hard for slope body to entirely failure. However, the soft rock continuing to creep can lead to a significant increase in the accumulative internal energy and expansion in local deformation. This process is the cause for instability and failure of the overall slope.