Abstract: The Yanlian landslide occurred on October 21—22, 2010 The slide mass cut off 24 oil transfer pipelines and the road from the factory to an oil tank, and buried part of the coal storehouse. The 34 oil tanks hanged over the top of the head scarp because of this. The landslide led to a suspending of the refinery work for a week and caused economic losses of approximately 700 million RMB. There was no rainfall or earthquake occurring before the slope failed, so the cause of the landslide is deeply concerned by the refinery managers and researchers. Site exploration shows that the sliding mass is the unsaturated-saturated loess material and groundwater is rich in the landslide and poor in the surrounding slopes. Further investigation shows that the water drops released from the vapor heating furnaces on top of the slope are the only source of groundwater. A pre-failure slope model is used to simulate the water infiltration process and the stress field. The slope stability is calculated with the shear stress and the strength along the potential sliding surface. The results suggest that rising of the groundwater level led by penetration of the water drops is the key factor imitating the landslide. A long term accumulation of the very little water drops infiltrating into the slope resulted in the rise of groundwater level and caused the slope failure.