Abstract: The change of soil and water mechanics caused by rainfall infiltration in loose soil is the key to affect stability. At present, most studies focus on the influence of particle size, content and other factors on slope failure. However, the research on the internal water-soil response and spatial-temporal evolution of slope stability is insufficient. Based on a field landslide case, this study explores the deformation and failure processes and mode of loose accumulation slope triggered by rainfall through the flume test, soil mechanics test, and theoretical analysis. The Van Genuchten model (VG model) is used to reconstruct the soil-water characteristic curve of the soil, and the mechanical change of soil and water in the slope and the temporal and spatial evolution of stability are mainly explored. The results show that: (1) The failure processes of the accumulation slope emerge in three stages, that is, the micro-fracture development stage, local failure stage and complete collapse stage, presenting the failure mode of “initial cracking-slope collapsing-plastic sliding”. (2) The volumetric water content and pore water pressure of slope increase rapidly during infiltration, while the matric suction between soil particles decreases or even dissipates, which promotes the development of slope failure. (3) The mechanical strength of soil decreases exponentially with the increasing volumetric water content. When the volumetric water content is 36.3%, the effective cohesion and effective internal friction angle are only 0.27 kPa and 3.39°. (4) Based on the limit equilibrium theory and the monitoring data of slope soil-water characteristics, the spatio-temporal evolution map of slope stability is constructed, which is in good agreement with the failure characteristics of the model test. The research results provide theoretical support for monitoring and early warning of accumulation slope under rainfall and disaster prevention and mitigation.