Abstract: Field geological investigations after earthquakes show that the effect of vertical seismic force is very evident, whereas only the effect of horizontal seismic force is concerned in conventional analysis of dynamic response of slopes. Collapsing and sliding responses of slope near epicenter and its running out process triggered by single and combined actions with time difference, local condtions and spatial heterogeneity of P and S seismic waves are elaborated. The formation mechanism and key controlling factors of the slope collapsing and sliding are confirmed. The result of numerical simulation shows that the slope collapsing and sliding are triggered by the combined action of seismic P- and S-waves, i.e. the coupled effect of vertical periodic tension and compression and horizontal periodic shearing. For the vertical tension of P-wave is dominant, tension and shear fractures would appear in slope body. On the other hand, combined action between periodic tension and compression of P-wave and periodic shearing of S-wave is the key controlling factor inducing slope collapsing and sliding on the conditions of known seismic tectonics, structure and tectonics of slope mass, weathering degree of rock mass and physical and mechanical parameters of slope body. At the same time, slope topography is the key controlling factor leading to collision and debris flow of slope mass fractured in latter process. It is of great theoretical and practical value in studying collapsing and sliding of slope triggered by seismic loads.