Abstract: To investigate the stability characteristics of slopes reinforced with anti-slide piles under extreme rainfall conditions. An analytical model was developed based on the upper-bound limit analysis method, incorporating rainfall infiltration and matric suction. By incorporating wetting front depth and matric suction, an upper-bound solution for the factor of safety was derived. The evolution of the safety factor under both short- and long-duration extreme rainfall scenarios was examined, along with a sensitivity analysis of key parameters influencing the optimal placement of anti-slide piles. The results indicate that the rate of reduction in the safety factor is positively correlated with initial matric suction. The effectiveness of pile reinforcement is highly dependent on pile location, with the optimal position located in the upper-middle portion of the slope. Under short-duration rainfall, the safety factor decreases steadily as the wetting front advances, exhibiting a relatively the reduction rate. In contrast, during long-duration rainfall, the safety factor declines as matric suction dissipates, with the reduction rate gradually decreasing over time. This optimum location is highly sensitive to variations in internal friction angle and slope inclination but shows low sensitive to changes in wetting front depth and matric suction. These findings provide a theoretical foundation for the design and disaster mitigation of anti-slide pile-reinforced slopes under extreme rainfall conditions.