[Purposes] This paper aims to study the mechanical characteristics of multi-row anti-slip piles for reinforcing the existing retaining dams, determine the most effective number of rows of anti-slip piles, and explore the weak zones reinforced with multi-row anti-slip piles and appropriate reinforcement steps under the influence of groundwater, so as to provide a reference for the application of multi-row anti-slip piles in retaining dam engineering. [Methods] A graded loading test equipment of multi-row anti-slip piles was designed. Under the background of the retaining dam reinforcement project of Xiaping Landfill, the model tests of unreinforced, single-row, double-row, and triple-row anti-slip pile-reinforced dams were carried out. The pile displacement and internal force distribution of different reinforcement schemes were compared. Next, full-scale models of the retaining dam reinforcement project were established to numerically simulate and analyze the weak zones of the dams under the influence of the most unfavorable groundwater level. The groundwater level control requirement for different numbers of piles for simultaneous construction was calculated based on the Coulomb earth pressure theory, and the recommended number of piles for simultaneous construction was given according to the actual engineering practice. [Findings] Multi-row anti-slip piles can effectively reduce the displacement of the dams, and the dams are gradually stabilized with the increase in the number of rows of anti-slip piles. When the anti-slip piles are changed from a single-row to a double-row form, the bending moment of the piles is reduced most significantly, and the reinforcement effect is not significantly improved when the piles are changed to triple-row anti-slip piles. In addition, the multi-row anti-slip piles can only effectively reinforce the downstream part of the dams, and additional reinforcement measures should be taken in the upstream part of the dams to enhance the safety reserves of the dams. [Conclusions] For this project, double-row anti-slip pile reinforcement can meet the safety requirements of the dams, but a triple-row anti-slip pile reinforcement scheme is recommended for providing adequate safety reserves. Skip-excavation operation is recommended during the construction, with at most five anti-slip piles constructed simultaneously.