The slip surface

which has different grades

is the base of the slope stability analysis and the methods for ascertaining it are different with the different slope structures. For countertendency soft rock slope，it can not be ascertained from the distribution of discontinuities as usual. Combined with FLAC3D and limit equilibrium method

the stability of countertendency shale slope with block cutting by discontinuities failure model is analyzed. Based on the field investigation

the deformation and failure mechanism is studied

the different grades slip surfaces are obtained from the analysis of the strain

stress and their increment pictures from FLAC3D analysis and the factor of safety is computed respectively. The prevention schemes are decided with the considering of the sub slip surface and the prevention effect is analyzed by aiming at the dangerous area. The safety factors of two dangerous areas

which are computed by shear strength reduction

indicate that the stability of the slope after prevention is good. The method used in this paper can be used as a reference to analyzing the stability of countertendency soft rock slope. The consideration of sub slip surface in prevention design has some practical guiding values