To reduce the safety risks of metro shield tuneling, the vulnerability theory and its literature are presented. The causes of vulnerability are listed based on the existing literature, typical accident cases, and the Delphi method. Further, based on the examined data and confirmed model from structural equation model, the obtained results are applied to a metro shield project in Foshan, China, and five crucial influencing factors (i.e., man, machine, material, method, and environment) are obtained using the importanceperformance analysis (IPA) to quantitatively evaluate a case project. The following are the findings of the IPA: (1) The premise of effective vulnerability reduction is establishing five crucial influencing factors in strict accordance with the specifications and construction environmental conditions. (2) Improving emergency support capabilities should be focused on to improve adaptability. (3) Taking only security measures required by the policy cannot effectively minimize the vulnerability, the design, monitoring plan, and management measures of the construction organization should be formulated in strict accordance with the specific construction situation. Finally, corresponding solutions are proposed in accordance with typical accident cases as well as metro construction codes and standards to offer suggestions for future shield tunneling safety control.