Abstract: Tunnels are key components of urban underground transportation systems, and their structural safety and service stability have a direct impact on operational safety; therefore, implementing long-term and continuous structural health monitoring is of significant engineering value. Brillouin optical time-domain sensing is a representative distributed fiber-optic monitoring technology characterized by long monitoring range, flexible deployment, and good long-term stability, and it has been increasingly applied to tunnel structural monitoring. Based on tunnel engineering monitoring practice, this paper systematically describes the fundamental principles and technical characteristics of Brillouin Optical Time-Domain Reflectometry (BOTDR) and Brillouin Optical Time-Domain Analysis (BOTDA), and summarizes their current applications in monitoring tunnel structural stress and deformation. On this basis, from the perspective of the coupled interaction among sensing cables, tunnel structures, and surrounding rock, the monitoring applicability and error characteristics associated with different tunnel structural forms and fiber deployment schemes are systematically summarized. In addition, a comparative analysis of BOTDR and BOTDA is conducted with respect to monitoring accuracy, spatial resolution, and adaptability to complex environments, thereby clarifying the engineering applicability of the two techniques under different tunnel conditions. The results indicate that Brillouin optical time-domain sensing enables fully distributed, long-term monitoring of tunnel structural stress and deformation, showing strong potential for tunnel operational condition assessment. Finally, future development trends of this technology are discussed in terms of adaptability to complex environments and data analysis methods.