Abstract: According to the relationship between deformation pressure and convergence of surrounding rock of excavation space, a formula for load of the surrounding rock for a circular cross section tunnel is deduced based on the Hoek-Brown failure criteria. Then it is extended to non-circular cross section tunnels using the equivalent circle method for tunnels. The formulae for the stiffness and resistance of composite supporting structures, which are composed of shotcrete, bolt and steel arch, are constructed based on the parallel model after the characteristic function for the supporting units (anchor, etc.) is deduced. A method to determine the starting point of the curve of the supporting structures is suggested according to the space effect of the tunnel surface. Based on the above-mentioned results, an approach for stability coefficient of the supporting structures is established considering the convergence-confinement method. The approach overcomes the defect that the empirical design method for the supporting structures based on rock mass classification cannot quantitatively evaluate safety degree of the supporting structures. Finally, the operation process of the proposed method is demonstrated through analysis of a case history and its validity is tested and verified preliminarily.