To evaluate the safety risks associated with the construction and operation of underground engineering, this study takes the complex cavern group of the “818 Project” as the research background. A two-level safety evaluation index system was established, including a first-level framework comprising four dimensions (human factors, materials, management, and environment) and a second level system consisting of 15 indictors, such as technical support, personnel quality, cavern seepage and leakage, safety inspection, and rainfall conditions. Four risk levels for cavern group construction and operation were defined: Level Ⅰ (inadmissible), Level Ⅱ (undesirable), Level Ⅲ (allowable), and Level Ⅳ (negligible). Based on these classifications, a two-level fuzzy comprehensive evaluation model for the operational safety of the “818 Project” cavern group was developed. Using the fuzzy evaluation matrices of the four primary indicators together with construction and operational data, the single-factor fuzzy evaluation matrices and index weights for both levels were determined through the analytic hierarchy process (AHP). The proposed model was then applied to predict the construction and operational safety of the cavern group. The evaluation result yields a grade value of δ=2.3445, corresponding to risk level Ⅳ , indicating a low probability of risk occurrence. The findings provide a scientific basis for safety assessment and risk management in the construction and operation of underground cavern groups.