Abstract: Long-term irrigation in agriculture in the Heifangtai area leads to the elevation of groundwater levels. At top of the poor-permeability silty clay layer, the thickness of saturated loess increases. Slope creep deformation induces a large number of loess landslides. Under the action of groundwater infiltration, landslide transforms the loess flow and moves ahead. To examine the deformation and failure mechanism of the loess slope, the stress path tests is designed under 8 kinds of confining pressures. The results show that the stress and strain mode of the saturated loess are in a strong strain-softening way and are of steady characteristics. The strength of samples totally loses and the loess fully liquefies under the confining pressure of less than 300 kPa, and the rest of the samples is partial liquefaction and the ability to resist deformation increases. The soil stress state can be divided into completely liquefied area and part of the liquefaction area. Deformation and failure characteristics of the slope are different because of the thickness of loess. In the interpolation calculation, when the thickness of loess is greater than the critical thickness (20 m), the slope behaves the sudden destruction. On the contrary, loess flow on the type of loess mud flow occurs in the slope. The results show that the reduce-loading is scientific in the Heifangtai area. The research results provide a theoretical basis for prevention engineering of landslides.