The installation of stabilizing piles has significant effects on the failure characteristics of slopes. A kinematical mechanism composed of rotational blocks is proposed for analyzing the stability of reinforced slopes. The plastic failure of the soil surrounding piles is considered by introducing velocity discontinuities on the pile plane. Objective functions are derived to determine the needed resisting forces or safety factors. Several example validations are conducted, and the effectiveness of the proposed method has been proven. The critical slip surface determined by the proposed method agrees well with the plastic region obtained through numerical analysis, particularly the plastic failure on the pile plane. Parametric studies indicate that local slope failure will occur when piles have close spacing and sufficient length. The optimal position of piles depends on the object to be determined, but it is generally recommended to place them between the toe and the middle-upper part of the slope. Additionally, the proposed mechanism is utilized to generate stability charts for quick evaluation of slope stability.