Abstract: Collapses and landslides in slopes with soft base are very common geologic disasters in southwestern mountain regions and the Three Gorges reservoir area of China. They are harmful. The upper hard rock weight,the weathering and water softening and the underlain by soft rock base can generate compression and horizontal plastic flow towards the free face. Therefore,the upper hard rock can generate tensile cracks. Ultimately they lead to collapses and landslides. A slope in Guizhou is examined. Its upper part has a height of about 150m and is a limestone cliffs. Its lower part has a thickness greater than150m and is a shale gentle slope. It is a typical slope of a gently inclined ramp within the weak base. This paper uses the finite element numerical simulation and bottom friction method of combining physical simulation. It analyses the slope of the body stress,deformation distribution and development process. Based on this model,the paper studies the weak base of slope and its deformation and failure mechanisms and provides the theoretical support for the weak base slope of geological disasters protection. The results show that the slope deformation and failure mechanisms dipping the base are of the three performance of a compressed plastic flow,tension crack and shear-cut.