Abstract: The basic theory and method of stiffness reduction and the implementation in FEM were introduced.The safety factor considering the stiffness reduction was smaller than that without regard to it because of that some points in slopes came into plastic state with the increase of strength reduction in finite element calculation,the plastic zone tended to expand under the constraint of the surrounding soil,but the expansion of the plastic zone became slow for the attenuated interaction among soil while the parameters ν and E were decreasing at the same time.The zone connected by Mohr-Coulomb and tension cut-off points was smaller than that without regard to the stiffness reduction,and these points concentrated nearby the potential sliding plane,and formed the shearing sliding band,so the calculated results by the FEM were not convergent,and the overall collapse occurred.Making use of the calculated results by the FEM,it was considered that the plastic zone developed from the slope toe to the top did not mean the overall collapse through comparison of the calculated results by the strength reduction FEM with and without of considering the stiffness reduction.