Abstract: During the operational period, shield tunnels are subjected to the alternating effects of factors such as the groundwater environment, cyclic train loads, and ground traffic loads, making them highly susceptible to the development of voids behind the tunnel walls. Such void diseases pose potential risks to the operational safety of the tunnel structure. Taking the void disease in operational shield tunnels as the research object, that parameterizes the void disease to describe its severity quantitatively. Using a metro tunnel as the engineering background, this study analyzes the modal characteristics and dynamic characteristic evolution laws of the tunnel structure under working conditions with no void damage and varying degrees of voids based on perturbation theory. Finally, the modal strain energy indicator (MSEI) is introduced to detect the location of voids. The results demonstrate that perturbation theory can effectively analyze the dynamic characteristics of voids behind shield tunnel linings, and MSEI can effectively detect the locations of voids. This study provides a theoretical basis for the detection, analysis of tunnel void diseases and monitoring of tunnel health.