The contribution of matric suction to the stability of unsaturated soil slope should be properly evaluated in order to meet the demand of practice. Firstly
Bishop’s and Fredlund’s strength equations for unsaturated soil are discussed
respectively. Then the strength equations expressed in three-dimensional effective stress space are applied to the strength reduction finite element method and the treatments of the matric suction are discussed. Finally
the FEM codes are implemented and a case of unsaturated soil slope stability is analyzed.