Abstract: The chemical-mechanical coupling effect of tunnel lining concrete under sulfate attack will lead to the degradation of its mechanical properties, and the degradation law is affected by many factors. A chemical–mechanical coupling method for accurately evaluating the time-dependent mechanical behavior of tunnel linings under sulfate attack is proposed. The improved diffusion-reaction equations for sulfate ions are obtained on the basis of the diffusion–reaction approach in combination with the mechanism of volume expansion under a sulfate attack and the influence of load on the concrete voidage. The constitutive response and damage parameters of concrete are calculated according to the volumetric strain caused by the external load and ettringite growth. Then, the evolution model for the bearing capacity of reinforced concrete linings under sulfate attack is established. A case study is conducted to analyze the degradation laws of strength of concrete and bearing capacity of linings obtained using the proposed method. The results demonstrate that the sulfate corrosion will significantly reduce the bearing capacity of the reinforced concrete linings, and the eroded lining is more prone to large eccentric damage. The proposed method serves as a reference for evaluating the durability of an underground structure in a sulfate formation.