This study aims to investigate the effects of antislide piles and cohesion anisotropy on seismic displacements of three-dimensional (3D) layered slopes. A discrete mechanism generated by the point-to-point technique is employed as the deterministic model, and the particle swarm optimization algorithm is used to determine the least upper-bound solutions. By combining the pseudostatic approach and Newmark's method, the yield acceleration coefficients ky and earthquake-induced displacements of two-layer slopes are further analyzed in varying positions of strong/weak layers, ratios of layer strength, reinforcement locations of piles, and anisotropy coefficients of cohesion. The results indicate that for the seismic slopes (strength ratio Sr = 1.5), displacement can be reduced by an order of magnitude after pile reinforcement; considering the anisotropy results in higher safety evaluations, typically, there is generally about a 65% reduction in the seismic displacement of Sr = 1.5 slopes when coefficient kc decreases from 1 to 0.7; the optimal pile locations in anisotropic slopes may be further away from the slope toe; the presence of a strong layer at the bottom of the slope is more conducive to slope stability than in the top, but it also makes the slope stability more sensitive to changes in layer strength ratio; the destabilizing/stabilizing effect of the weak/strong layer at the slope bottom is most pronounced at low values of its proportion; switching the strong layer from the bottom to the top, the maximum values of ky experience a 25%-40% reduction, while this percentage would be magnified when calculating its impact on displacement. Moreover, different from single-layer slopes, layer heterogeneity may also result in nonuniqueness in the optimal pile locations.