Abstract: Great earthquakes in mountainous areas usually cause large numbers of landslide dams. For example, at least 257 landslide dams formed during Wenchuan Earthquake in 2008. Lots of aftershocks occurred after the major shock, which might influence the safety of these landslide dams. This paper presents the studies of large-scale shaking table tests on the breach mechanism and process of landslide dams under the coupled effect of aftershocks and water. Two groups of shaking table tests were conducted to simulate the behaviors of two types of landslide dams：one with cohesive materials and small particle size(Dam I) and the other without cohesive materials and with large particle size(Dam Ⅱ). The shaking table tests were conducted under different water depths. The following conclusions are drawn：(1)The main failure mode of landslide dams under the coupled effect of aftershocks and water is overtopping. The breach process is that：seismic force causes the subsidence of the loose landslide dams, seepage of water enlarges the subsidence value, finally, water level rises and overtops the dam crest and the dam fails by water erosion. (2)Earthquakes may not directly cause the failure of landslide dams. The main influence of earthquakes on landslide dams is causing subsidence of dam crest. The subsidence value under the coupled effect of aftershocks and water is larger than that under the effect of either factor. The subsidence induced by the earthquakes may bring forward the overtopping of landslide dams.(3)The subsidence of Dam Ⅰ is larger than that of Dam II under the coupled effect of earthquakes and water, which shows that landslide dams composed of rock and soils with larger particle size are more stable.