Failures of treated slope occurring in China are at a consistently increasing rate, leaving the huge number of treated loess slopes calling for post-evaluation, however, no mature technique is in place. Depended on an loess slope in Shaanxi province treated by slope-cutting, indoor geotechnical and model tests were conducted, revealing the rainwater infiltration characteristics and pressure varying characteristics inside the slope, the results of which were then adopted to perform the post-evaluation of the treated slope. The results showed that the rainwater scouring effect on the loess slope surface attenuates gradually, and enters a steady stage after the first year of rainfall. The rainwater preferentially penetrates the platforms with gradually attenuating rates, however the wetting front can not be deemed as the boundary between the saturated and unsaturated areas, as the most parts of the model slope were indicated unsaturated by the pore water pressure sensors. Caused by the in-situ stress release, the soil pressures don’t increase but decrease sharply at the start of the rainfall. The displacements mainly occurs in the first two years of rainfall, following by steady periods. The model test results and investigation results were then used to conduct the post-evaluation of the prototype slope, which formed a post-evaluation frame relevant to other slope post-evaluations.