Gully Stabilization and Highland Protection (GSHP) techniques are useful in preventing gully erosion and have been widely utilized in the Loess Plateau. Rolling backfill is used to fill ditches in remolded loess, which is an important part of gully stabilization and highland protection, but destroys the original loess structure and changes the circulation of groundwater and surface water leading to a rise in groundwater. Groundwater rising is an important factor for filled loess slope instability and can induce landslides. A test device was designed to study the process of water infiltration into the filled project and the failure process of the filled loess slope due to groundwater rising. First, the groundwater was uniformly infiltrated with water, then preferential seepage with the deformation and cracks appeared in the slope. The pore-water pressure response to the groundwater infiltration and the pore-water pressure in the front of the slope body sharply increased, especially near the sliding surface, while the pore-water pressure at the back of the slope sharply decreased during slope failure. The failure process of the experimental slope can be divided into three stages: settlement deformation, collapse deformation, and slope toe slide-flow or regressive failure. In the first and second stages, the deformation is vertical displacement as slope settlement, and the third stage deformation is mainly horizontal displacement in the direction of the free surface of the slope body. The filled slope failure is due to groundwater infiltration with suffusion erosion, saturated softening, and infiltration dynamics.