Abstract: Three-dimensional structure and unsaturated condition have essential influences on the evaluation of slope stability. In order to study the main influencing factors on the stability of unsaturated soil slopes, an extended three-dimensional model for standard tests is taken as the example, then based on elasto-plastic constitutive model and strength criterion of unsaturated soils, the numerical simulations of slope stability are carried out. From the two aspects of external and internal factors, the influencing rules on the stability of three-dimensional unsaturated soil slopes are analyzed by discussing the variation of negative pore water pressure distribution and underground water table caused by rainwater infiltration as well as the depth of sliding surface and the strength parameters. The results show that the three-dimensional method can reflect the spacial stress state and the shape of sliding surface, and that the influence degree of each analytical factors on the slope stability is successively the variation of , the decline of suction due to water infiltration and the depth of sliding surface. With the depth increase, the effect of increases, and the water infiltration has obvious influences on the shallow landslides.