The stress-deformation law and the structure-soil interaction of chair-shaped pile(CSP) retaining structure on soft-rock steep slope under stepwise loading on the subgrade surface are studied by large-scale model test. According to the experimental conditions and stress states, the design and calculation method of CSP are proposed. The test results show that the spatial structure properties of CSP can efficiently control the deformation and reduce the pile stress; the bending moments of main and side piles have little differences; the maximum bending moment is located at the slope surface; and the pressure of pile side rock is related to the deformation of piles and the deformation modulus of rock. The toppling failure of CSP would not occur generally; and the shallow layer failure is the main failure of soft-rock slope. Based on the analytical solution of elastic foundation beam, the change and distribution rules of internal forces of CSP could be described well. The study results have a good reference value to correctly analyze the anti-slide mechanism, design and calculation of CSP retaining structure.