Abstract: The current methods for evaluating tunnel lining defects do not quantitatively account for the impact of defect spatial location on structural safety. There is an urgent need to establish a lining safety evaluation system that can quantify the spatial influence of defects to enhance the accuracy of tunnel structural safety assessment. Through finite element numerical simulation and multi-index normalization fusion, a comprehensive safety index calculation formula for tunnel lining structures is constructed, considering crack geometric characteristics, structural internal forces, and cross-sectional strength safety. Based on this, the safety of tunnel linings is classified into four levels: safe, relatively safe, relatively unsafe, and unsafe. The results show that: (1) A tunnel lining spatial safety evaluation method and indicator system are proposed, which includes the normalization, weight allocation, and weighted fusion of seven indicators, such as crack geometric dimensions, structural internal forces, and cross-sectional strength safety coefficients. The safety of tunnel lining structures is classified into four colors and four levels based on the three thresholds of 0.48, 0.70, and 0.25; (2) Engineering applications demonstrate that, compared to single-indicator evaluation methods, the comprehensive safety index can accurately identify differences in the safety of tunnel lining structures caused by cracks at different locations, effectively supporting differentiated maintenance and decision-making. The research findings are applicable to tunnel lining safety assessment and provide support for the revision of the static and single-indicator evaluation methods in current specifications.