Abstract: When the metro is in operation, there are increasing longitudinal nonuniform settlements of shield tunnels due to various interior and exterior causes. Therefore, some expansion of shield tunnel segment joints develops in varying degree and the water resistance deteriorates. By using the 4th order B-spline interpolation curve to fit monitoring data and calculate additional longitudinal curvature, the degree of nonuniform settlements can be accurately reflected. Then considering the additional curvature radius, geometrical dimension of segment and longitudinal stiffness ratio, that means aleatory uncertainty and epistemic uncertainty are all considered, an interval Monte Carlo method at different levels of significance is developed to estimate the probability of shield tunnel segment joint failure. Grading the upper bound of the failure probability using four level assessments can directly reflect the operational performance of the segment joints. Inspection and evaluation results are compared and show good consistency. It is proved that the proposed method can provide guidance for the maintenance of shield tunnels in soft soils.