This paper is to determine the spacing of cantilever piles for stabilizing slope more reasonably. The defects of existed analysis models for cutting slopes are discussed. A reversely trapezoidal compressed zone is assumed to present behind a pile. This zone is the arch foot related to soil arching on both sides of the pile. Some control conditions are given for calculating rational spacing between two adjacent piles. These conditions include (1) static equilibrium equation between slope thrust on the soil arching and resistance on its two end sections near the two piles

(2) strength principle of the point at internal edge of medial cross-section of the soil arching

(3) the strength condition of two end sections of the soil arch

(4) calculation width of the pile due to its spatial resistance effect and (5) compatibility of deformation between the pile and the behind soil. The equations to determine the spacing are given and can be solved with iterative and trial and error calculation methods. Results of an engineering example quantitatively show that the spacing between two adjacent piles nonlinearly increases as the cohesion or internal friction angle of soil behind piles increases. It nonlinearly decreases as the upslope landslide thrust on the piles increases. In addition

the effect of the cohesion on the spacing is more sensitive than that of the internal friction angle. The proposed method can be suitable for both cohesive and noncohesive soil.