The core problem of tunnel stability in the process of tunnel excavation lies in the controllable degree of stress release of the surrounding rock stratum, and stress release rate not only affects the judgment of the tunnel support timing, but also has a significant impact on the lining stress and stability, so determination of the critical value of the stress release rate still lacks detailed and reliable research. In this paper, the influence degree of different stress release rates on the stress of tunnel lining is analyzed by elastic-plastic element method, and the critical value of stress release rate corresponding to the cracking of tunnel lining is determined. The results show that the horizontal stress of the lining gradually decreases with the increase of the stress release rate, and the critical value of the stress release rate is determined to be 61% based on the design value of the tensile strength of the lining concrete. The critical stress release rate can reasonably determine the construction timing of tunnel lining, to ensure the tunnel lining can maintain a stable working state.