Abstract: The collapsing and sliding response of Xinzhong slope in Beichuan County and its collapsing process triggered by the single and combined action with time difference and the regionality and spatial heterogeneity of P and S seismic waves are studied. The formation mechanism and key factors are determined by applying DEM numerical simulation. The results show that the initial collapsing and sliding of the slope in running time, i.e. 8 seconds of numerical model, is triggered by the combined action of horizontal and vertical tensions caused by P seismic waves because of their relatively long distance from the initial epicenter inducing larger difference, i.e. 15.21 seconds in time, which P and S seismic waves consume from the hypocenter to the slope. What’s more, the horizontal tension plays a superior role. Ejecting and flowing of the broken slope mass is triggered by the combined action of P and S seismic waves. Secondly, the combined action between horizontal and vertical tensions of P waves is the key factor inducing the collapsing and sliding of the slope under the known seismic tectonics, structure and tectonics of slope mass, weathering degree of rock mass as well as the physical and mechanical parameters of slope body. At the same time, the slope topography is the key factor leading to collision and debris flow of the slope mass fractured in latter process. Finally, the amplification effect of parameters in dynamic response of the slope shows that the amplification coefficient of horizontal acceleration is larger than that of vertical acceleration. The horizontal velocity and the vertical velocity decrease one by one, and this trend is consistent with the key factor inducing slope fracturing, i.e. horizontal seismic loads play a superior role. It provides a new method for studies on the initial collapsing and sliding of slopes triggered by seismic loads.