Abstract: To clarify the reinforcement effect of steel strips on tunnel linings under coupled multiple defects, three typical defect types—insufficient lining thickness, concrete degradation, and voids behind the lining—were investigated. Based on the load-structure method, a numerical model of the lining was established to analyze the variation of sectional safety factors under different coupled defect conditions, and the safety performance of linings reinforced with steel strips of varying thicknesses was further evaluated. The results indicate that: when a single defect occurs,such as insufficient local lining thickness reduced to 60% of its initial value, concrete performance degraded to 60% of its initial value, or the presence of voids alone, the sectional safety factors of the lining still meet the code requirements. However, when insufficient thickness and concrete degradation occur simultaneously at the arch crown, arch waist, or arch foot, the safety factor of the defective section all falls below the code limit of 2.4. When insufficient thickness and voids couple at the arch waist, stress redistribution reduces the safety factor of the arch crown to 2.3.When all three defects act simultaneously at the arch crown, arch waist, or arch foot, the safety factors drop to 2.1, 2.0, and 2.0, respectively. For coupled insufficient thickness and concrete degradation at the arch crown, reinforcement with a 6 mm steel strip restores the safety performance to meet the code requirements. For coupled insufficient thickness and voids at the arch waist, reinforcement with a 4 mm steel strip increases the arch crown safety factor to 3.0. Moreover, 4 mm steel strip reinforcement ensures that the sectional safety factors meet the code requirements even under the coupling of all three defects.