Abstract: Soil arching may be generated below excavation base. This kind of soil arching is featured with different boundary conditions of mechanism and displacement compared with that above trapdoor, of which the development orientation is the same as that of soil gravity stress. To investigate the characteristics of the soil arching below excavation base, the centrifuge modeling of excavation with dry sand layer is conducted. Thereafter, a sequence of numerical analyses of the soil arching below excavation base are carried out under different excavation depths and widths. The research shows that the differential deformation and stress transfer are observed and the soil arching below excavation base is confirmed. The excavation base is divided into the loosened zone and the arching zone. The loosened zone exhibits a significant decrease in the relative density, while the arching zone accounts for about 80% basal heave. As the key to the formation and evolution of soil arching below excavation base, the depth and width of excavation are positively correlated with the range of the loosened zone and arching zone. The conclusions can provide a reference for the prediction of excavation-induced ground response and the deformation control of the underlying existing underground structures.