Many loess high-fill slopes have been constructed in the Loess Plateau of China, which are susceptible to shallow diseases and disasters owing to water migration and evolution. The existence of a slope surface profoundly affects soil moisture dynamics, thus potentially altering the slope instability. According to long-term, multi-point, and multi-depth on-site monitoring, shallow soil moisture's migration and evolution characteristics under slope effects were investigated. The influence of the microtopography on the slope effects is also clarified. The results showed that the characteristics under sloped conditions significantly differed from those under flat terrain conditions. During water infiltration and redistribution, the sloping topography shifts the depth of influence of rainfall infiltration downward; the lateral flow duration and the peak of the change rate of moisture content (CRMC) at the slope step were significantly smaller than those at the slope face. During the drainage stage, the slope effect enhances the draining capacity and range of soil layers, with the slope step exhibiting greater draining efficiency. Besides, the slope effect reduces the magnitude and amplitude of soil water potential gradients (SWPG), thereby weakening the intensity of driving force evolution. Among the factors influencing the slope effect, large rainfall events and root plant development promote the slope effects, whereas high initial water content and shallow groundwater tend to suppress it. These findings are of great significance for advancing the understanding of slope soil moisture migration patterns and ensuring the stability of shallow slope layers.