Abstract：The stability of bedding rock slope is mainly affected by two factors，which are physico-mechanical properties of slide face and groundwater pressures. Based on analysis of formation and evolvement of rock slope bedding-slip failure due to hydraulic drive，the effect mechanism of groundwater on bedding rock slope stability is discussed. It is pointed out that groundwater flows through the passage that consists of the slide face and the top splay fracture of a rock slope produces static water pressure of splay fracture，flotage and haulage of slide face. Equations for calculating the critical water highness in the splay fracture and the critical rainfall intensity are developed. It is shown that：(1) water pressures above increase with increasing the water highness of the splay fracture；(2) the slope will lose its stability once the water highness of the splay fracture reaches to a critical value；and (3) the water highness of the splay fracture is linear with the rainfall intensity. The bedding-slip failure criterions of rock slope are put forward at length.
