Landslides caused by earthquakes pose a great threat to life, the environment, and the economy. Present studies on slope stability under earthquakes mainly focus on the failure modes of single sliding surfaces, while studies on slope stability with multiple potential sliding surfaces are comparatively obscure. A numerical simulation is conducted on the seismic stability of different slopes by using the finite difference software FLAC. The evolution process of sliding surfaces and the distribution characteristics of permanent deformation of homogeneous soil slopes, layered soil slopes, and soil slopes with weak interlayers under different earthquake intensities are compared and analyzed. Results reveal that the sliding surface of homogeneous slopes caused by earthquakes exhibits a single sliding surface, and the increase in seismic intensity only leads to an increase in permanent deformation along the sliding surface. For heterogeneous slopes, seismic action may also trigger local sliding deformation at the soil interface, and the sliding surface initially formed under seismic action is consistent with the most dangerous sliding surface corresponding to the minimum safety factor obtained under static conditions. In addition, a complex interaction exists between the shallow and deep slope deformations and failures caused by earthquakes. If the shallow sliding occurs first, further increase in ground motion can easily induces deep slope sliding; if the deep sliding occurs first, then plastic deformation affects the propagation of seismic inertia force to the upper slope body; thus, the further sliding deformation of the shallow slope is relatively difficult to trigger.