Abstract：The triaxial test instrument for unsaturated soil controlled by stress and strain is used to measure the substrate suction and volumetric water content of unsaturated soil. The permeability coefficient of the unsaturated soil can be got from the concrete form of the Mualem equation which is deduced based on the relation between the soil-water characteristic curve equation and the permeability. The cohesive strength，internal friction angle and the internal friction angle changing with suction can be also got from the triaxial test on unsaturated soil in the laboratory. With the finite element method，the characteristics of the seepage field in the Yellow River lower reaches which is a representative unsaturated slope under the rainfall and flood condition are analyzed systematically. Also the safety factors influenced by the seepage field of unsaturated soils under the rainfall and flood are analyzed with the method of GLE which is a kind of limit equilibrium method not considering the effect of scour. The factors including the intensity of the rainfall，the permeability coefficient and the duration of rainfall and flood and the relationship between them are significant for the computation. By analyzing，the corporate influences of rainfall and flood infiltration on the safety of slope stability are analyzed；and the results show that the effect of rainfall and flood is complex and important for the safety of the river levee. The conclusions drawn from the study on the Yellow River lower levee during the rain and flood have practical significances for the hydraulic engineering.
