Check dam engineering is usually arranged in channel of deformation zones of debris flow. And it plays a role of retaining sediment, raising erosive base, slowdown slope of gully bed and stabilizing slope and fixing bed. Combined limit equilibrium method, the mechanism of cross-feed action between check dam and debris flow, upper shallow landslide is discussed in this paper. The influence of different trapped sediment thickness, the erosion of debris flow to slope toe and different height of water storage after dam on upper shallow landslide is calculated and analyzed. Stability of landslide at different location in the direction of trapped sediment is briefly described. The results show as follows. ¡ð1The trapped sediment after dam can stabilize slope, but the influence on increasing stability is little. On the other hand, slope mass sheared and shear opening elevation decrease landslide scale, and to some extent decrease the sediment source of debris flow. ¡ð2The most dangerous slip surface has great changes after water storage. The shear opening gradually reduces from slope surface to water level below. This leads to landslide scale increase and further increase sediment source in the debris flow gully. So the occurring scale of debris flow increases. ¡ð3The location of landslide is different in the direction of trapped sediment, gully erosion and trapped sediment thickness have different response to it. The nearer to check dam, the bigger trapped sediment, and the better landslide stability. Inversely, the farther away from it, the bigger possibility of erosion is, and the weaker stability.