In order to explore the deformation and failure mechanisms, as well as degradation characteristics of silt slopes under rainfall conditions, a large-scale slope model test apparatus was designed with silt slopes as the research subject. Multi-sensor internal monitoring and 3D laser scanning technology were applied. During slope instability under a rainfall intensity of 30 mm/h, data on moisture content, pore water pressure, soil pressure, and deformation and failure characteristics at various slope locations were collected. Results indicate that sensors at the slope toe have the fastest response, showing the highest rate of change. Rainwater accumulates at the slope toe, causing horizontal seepage, which leads to rapid increases in moisture content at the toe and lower middle sections of the slope, along with a reduction in soil shear strength. Under rainfall intensity conditions, the deformation and failure of silty slopes initiate at the slope toe, where small-scale collapses first occur. These progressively develop into transverse through-cracks, accompanied by minor-scale failures that extend upslope. Ultimately, these processes lead to overall slope failure. The findings offer theoretical insights to support engineering construction and protection in silty slope regions.