Abstract: The non-continuous retaining structures such as anti-slide piles rely on the soil arching effects to provide support safely and economically in slope engineering. Considering the significant differences in the mechanical properties of sands, to reveal the mechanism and evolution patterns of horizontal soil arching between piles in sand slopes, the discrete element method (DEM) is used to simulate the formation process of horizontal soil arching. On the basis of the traditional force chain analysis, it is proposed to study the formation process of soil arching by screening high stress particles. Furthermore, the analysis of the soil arching effects under different conditions from a microscopic point of view is conducted to reveal the evolution process of "stress arching" and "displacement arching". The results demonstrate that the dynamic evolution of horizontal arching in both dense and loose sands can be divided into three evolutionary stages, corresponding to the shear behaviors of the two sands, i.e., strain softening and strain hardening phenomena, which reveals the evolution patterns of the soil arching effects in the sand slopes. Additionally, the influences of macro-micro DEM simulation parameters on the arching process and performance are discussed. The results indicate that the arching span has the greatest impact on the load transfer efficiency.