Current studies on the three-dimensional （3D） large deformation analysis of slopes with reinforcement structures remain limited. In this study， a 3D numerical model for a slope reinforced with anti-slide piles is constructed using the material point method. The failure modes of the slope with anti-slide piles are analyzed， and the effects of the pile length， location， and spacing on slope failure are also discussed. The results show that， when the anti-slide piles are located at the slope toe， the soil above the anti-slide piles is prone to local failure， inducing overtopping and sliding. Increasing the pile length reduces the area of the plastic zone， but exacerbates shallow sliding and increases runout. When the anti-slide piles are located in the middle of the slope， the displacement of the slope after failure is the smallest， and the reinforcement effect is the best； however， when the pile length is roughly the same as the depth of the potential slip surface， the presence of piles may lead to a longer runout distance after failure. The increase of the pile spacing causes the plastic flow of the soil between the piles. When the anti-slide piles are located at the slope crest， the soil beneath them is easily dislodged and slides and the reinforcement effect is poor.