Abstract: The stability of the soils between unbaffled cantilever anti-slide piles should be considered during design. Based on model test results, a three-dimensional sliding surface model for the soils between cantilever anti-slide piles is established. The upper bound limit analysis method is used to obtain the maximum height of free face of the soils. The strength reduction method is combined with the upper bound limit analysis method to calculate the stability coefficient of the soils between piles. Both methods can be used to estimate the instability area and the volume of slumped soils. The maximum height of free face of the soils and the stability coefficient of the soils between piles calculated by the proposed method are compared with the experimental results, and the correctness of the proposed method is verified. Using the single variable method, the effects of the free face height h, free face width w, internal friction angle φ and cohesion c on the stability of the soils between piles are analyzed.