Fine grains migration is a primary cause of landslides and debris flows. This study investigates the effect of fine-grain migration on slope failure through flume experiments, focusing on the spatiotemporal characteristics and mechanisms of slope stability. A series of artificial rainfall flume experiments with varying rainfall intensities and slopes were conducted using soil samples collected from Wei Jia Gully. The experiments monitored pore-water pressure, grain migration, and failure sequences. Grain-size distribution parameters (mu and Dc) were analyzed to understand the migration path and accumulation of fine grains. The experiments reveal that fine-grain migration significantly alters soil structure, leading to random blockage and interconnection of internal pore channels. These changes result in fluctuating pore-water pressure distributions and uneven fine-grain accumulation, critical factors in slope stability. Slope failures occur randomly and intermittently, influenced by fine-grain content in runoff and resulting pore-water pressure variations. This study highlights that fine-grain migration plays a vital role in slope stability, with significant implications for predicting and mitigating slope failures. The stochastic nature of fine-grain migration and its impact on soil properties should be incorporated into predictive models to enhance their accuracy and reliability.