Abstract: A 20m high slope lies in construction site of an energy company.The mine slag was stacked 10 to 50 years ago and wholly belongs to Triassic soft sandstone and mudstone.The slag shows weathered earthy and strong weathering state.The sandstone fragments can be promptly crushed by hand.The mine slag shows loose structure,poor sorting,weak adhesion and strong permeability.The slag composing the slope was treated with dynamic compaction.But,many positions of the slag slope still slid and collapsed during the rainy season in 2010.The landslide sites were located in the lower slope.This paper examines the landslide mechanism and deformation characteristics of the dynamically compacted slope highly filled with slag under rainfall infiltration.It uses elastic-plastic mechanics finite element method,unsaturated fluid mechanics and other theories.The corresponding numerical model for displacement-unsaturated seepage coupling is set up.Based on the numerical model,displacement field,seepage pressure distribution,volume water content and safety factor are studied in detailed.The numerical results indicate: (a)with continuous rainfall,the slope safety factor significantly reduces; (b)because of the lower permeability after dynamic compaction,seepage positive pressure focuses on the top of the slope within a certain depth and gradually increases and tends to stabilize under continuous rainfall.But the maximum negative seepage pressure value basically keeps stable and negative pressure zone shows diminishing.This shows negative pressure has a limited impact on slope filled with slag after dynamic compaction.Emphasis is to take good drainage measures within a certain depth range at the top of slope to reduce seepage positive pressure; (c)vol.water content gradually increases to saturated status; (d)shear failure occurs at the toe of slope under continuous rainfall,leading to collapse in the lower part of slope.The research results have an important reference value for studying on stability of slag-soil mixed slope,such as gangue hill,tailing dam,roadbed primed with gravel,et al.