There are the wide alternant distribution of basalt and diatomite in the basin and highland in ShengXian.The layers are nearly flat.With the rapid development of the engineering actions in the highland with particular stratigraphic sequence,because of the buildings at the back of the sliding body and the cutting slope at the front,the pushing force of rock and soil in slope increased,but the anti-sliding force weakened.On the other hand,during the rainfall surface water immerged into the layer interface of the diatomite along the unloading cranny, resulting in the diatomite becoming soft after absorbing water and its shear strength lowered.At the time,the water level went up,the dynamic water pressure and uplift pressure increased,the anti-sliding force continued to reduce.Therewithal,the landslides occurred along sliding surfaces with small tilt angle.The analysis on the formation mechanism of landslip can provide basis for controlling the landslide.