Abstract: Abstract: Subsurface flow, constituting a critical component of slope runoff, plays a key role in the hydrological cycle and soil erosion processes. This article systematically reviews research advances in subsurface flow, summarizes its formation and development mechanisms, existing monitoring methodologies, key influencing factors, and emphatically expounds the driving effect of subsurface flow on soil erosion. The formation and development of subsurface flow depend on the "rainfall-infiltration" at the surface, and its migration process can be divided into matrix flow governed Darcy's law and preferential flow dominated by macropores. Research methods mainly based on experimental observation techniques (such as dye tracing method and computed tomography) and numerical simulation approaches (Richards equation, storage-discharge model, etc.) can quantitatively track the dynamics of subsurface flow and help reach a basic consensus in specific fields. However, individual methods still exhibit significant limitations. The subsurface flow process is jointly regulated by soil properties (texture, pore distribution, hydraulic conductivity, etc.), rainfall characteristics (intensity, duration, pattern), and topographic/vegetation conditions (slope gradient, aspect, root distribution characteristics), thus exhibiting strong spatiotemporal variability. Furthermore, subsurface flow exacerbates soil degradation through mechanisms including soil structure alteration, rapid induction of pore water pressure changes, and initiation of gravity erosion, thereby forming compound erosion effects with surface runoff. Future research should deepen understanding of the interactions between "interflow-surface flow-groundwater" in heterogeneous soils, prioritize synergistic effects of multiple factors and their variations under extreme conditions, and optimize hydrological models by integrating dynamic monitoring, thus providing a more robust theoretical foundation for watershed water security and soil erosion control.