Abstract: In order to guide the treatment work of “4·17” landslide of top slope in Pingzhuang Western Surface Coal Mine effectively and realize the safety production, based on the engineering geological conditions in sliding area, the evolvement characteristics of horizontal and vertical displacement were studied by the analysis of the monitoring data and the displacement vectorization, then the position and the shape were obtained, the mechanic mechanism was revealed and the formation conditions and the predisposing factors were determined. It is shown that the formation mechanism of “4·17” landslide is translational gliding mode, its failure mode is cutting-bedding and the sliding surface is composed of counter-tilt weak layer A, a near-vertical back wall and the sheared arc, that the main factors causing the landslide include boundary effect of the weak layer, the supporting role of the diabase, the damage of the integrity of the rock mass, unloading effort caused by surface mining and the plan form, in which, the predisposing factor is the unloading effort caused by surface mining.