Abstract: In order to study the mechanical properties of undisturbed loess slope under different circumstances in Jingyang county of Shaanxi Province, two humidification experiments are conducted. The constant water content tests are operated to observe the strength and deformation characteristics under different water contents (humidify with no stress conditions) and confining pressures by obtaining the value of φ^b in the shear strength formula of Fredlund’s double stress state variables, and a practical shear strength formula for the water content is derived by using FSY30 type strain controlled triaxial apparatus for unsaturated soils. The other tests are the experiments under different confining pressures and partial stresses in which cuts of the undisturbed loess are operated twice before and after the flooding to saturation. The two experiments reveal: (1) The stress-strain curves of loess in this region takes a hardening type according to the data analysis from the two tests; (2) Based on the constant water content tests, the water content and initial matric suction are hyperbolically related, and the matric suction shows no significant changes in the process of shearing. And the increase of water content has larger influence on the decrease of cohesion of shear strength index than the impact on internal friction angle; (3) On the basis of the second experiment, the strength of specimens decreases significantly after flooding which has little effect on the stress-strain curves. The lower the partial stress when humidification takes place, the lower the stable partial stress values.