Under the combined impacts of the operation time, design concept, and construction technology, extensive damage has occurred in tunnels built in China during the early stages of rapid development. Therefore, relevant research on tunnel damage is of urgent importance. This study takes the Liupanshan Highway Tunnel on G312 in Guyuan City as a case study, and uses field investigations, radar scans, and other methods to investigate the occurrence of a series of defects in the tunnel, including lining splitting, water leakage, and tunnel bottom damage, to analyze the damage characteristics and occurrence mechanism in detail based on both external causes and internal causes. From the results, by combing relevant materials both in China and abroad with the engineering characteristics, a comprehensive management method for reinforcing and strengthening damaged tunnels with a reinforced concrete umbrella arch is proposed. At the same time, considering the degradation in the bearing capacity of the existing lining structure and utilization degree of the bearing capacity of newly increased reinforced concrete umbrella arch, this study performs a theoretical analysis of the calculation for the safety factor of the reinforced damaged tunnel. The calculation results show that the reinforced Liupanshan Tunnel is in a secure state, which can provide references for similar projects in the future.