Abstract: Guantan landslide is a typical anti-dipped rock slope with soft foundation,a result of combined action of Wenchuan earthquake and rainfall after the earthquake.This paper built numerical analysis models of a slope with or without soft foundation.It revealed influence induced by soft foundation to evolution of stress field and extending trend of rupturing process of the slope during earthquake dynamic response process.Calculated result shows that before the failure of the slope,the existence of soft foundation can reduce the role of earthquake dynamic effect to a certain extent,which is positive to slope stability.But once the slope failed,the existence of soft foundation may intensify extension and coalescence of rupture surface,and finally form landslide.