<p>Complex environmental factors contribute to the degradation of tunnel surrounding rock and supporting structures, as well as structural damage under external loads. Accounting for these factors is critical in tunnel time-dependent system reliability analysis. This study develops a mechanical model that incorporates the time-dependent degradation of surrounding rock and supporting structure, with particular attention to three key factors: degradation of the surrounding rock, degradation and damage of the supporting structure. Based on the proposed model, a time-dependent system performance function is established considering three failure modes. The results demonstrate that the degradation coefficient <i>δ</i> exerts the most significant influence on all failure modes, with its independent effect increasing the failure probability associated with insufficient support strength by up to 1656.49%. The combined influence among parameters further amplifies the failure probability. Among them, the combined influence of the degradation coefficient <i>δ</i> and the damage coefficient <i>D</i>_<i>e</i> of the supporting structure is the most pronounced, leading to a maximum increase of 3301.38% in the failure probability associated with insufficient support strength. In the early stage of service, tunnel system failure is predominantly governed by insufficient support strength, whereas in the later stage, both excessive carbonation depth and insufficient support strength become critical contributors. The study indicates that ensuring long-term tunnel safety requires prioritizing the enhancement of support strength during the construction phase, as well as emphasizing the monitoring of carbonation depth and the control of lining damage accumulation during the operation phase.</p>