Abstract: This paper is based on the field survey and laboratory physical simulation in Kualiangzi landslide in Fengdian in Zhongjiang County. It finds that the slipping of the landslide can induce secondary tensile cracks or even through breakthrough. It combines the history of the landslide deformation with the force analysis. It demonstrates the generating process of tensile cracks and the breakthrough in sliding zone between tensile cracks, and puts forward the theory of multistage horizontal sliding in U-shaped slot model. It compares the study of multistage horizontally pushing landslide in Xuanhan county. It analyzes the formation mechanism and cause of multistage rift trough on rear edge. It compares the two different existing models of activating and motion styles, i.e.,pull-back style and push-forward style. It then establishes the geological mechanism models based on analysis of lithology, structural fissure development, inducing sliding water head height, velocity and water head height changes.