Aiming at the influence of pile foundation on bank slope stability,we analyze the influence of pile spacing,pile edge length and pile length on bank slope stability by means of numerical simulation.The results show that the ratio of pile edge length(pile diameter) to pile spacing determines the effect of pile foundation on bank slope stability based on conditions of the same bank slope and the freedom of pile top.For a specific soil layer,there is a margin ratio(diameter-distance ratio) value,which makes the pile foundation play an optimal role in the stability of bank slope.With the same size and spacing of piles,simply increasing the length of piles in the embedded soil layer cannot improve the effect of pile foundation on bank slope stability.