Abstract: The instability of a cut slope at Yuanjiawan section of Lan-Lin expressway is typically controlled and influenced by human activities, under the influence of obvious neotectonic movement, strong fold and fault structures, formed in dip bedded sandy conglomerate intercalated with shale of broken loose structure and serious surface weathering. The paper employs the analysis methods of engineering geology combined with Flac3D numerical simulation and analyses the sliding characteristics of repetition, succession, similarity and gradual increase, as well as the damaged form of independency and variety, because of a variety of the transformation forms of the human activities. The results show that the instability is characterised by evolutional process of continuously increasing damaged scale at the cut slope by human beings and gradually developed to the present natural state.