Abstract：Based on the geometrical meaning of structural reliability index，the reliability optimization model of segments lining in shield tunnel is proposed. Furthermore，the program is developed according to complex optimization algorithm. The numerical example is provided to demonstrate the better efficiency and accuracy of the optimization model，which avoids the performance function¢s partial derivative to the random variable，than those of first-order approximation methods. The value of equivalent standard normal distribution variable at checking point is expressed with the checking point coordinates and the statistics value of original random variable，which avoid the R-F(Rackwitz R. and Fiessler B.) equivalent normal transformation of each iterative calculation at checking point. In the example analysis，the optimization model is very suitable to acquire the reliability index of segments lining in shield tunnel where the performance function is highly nonlinear and implicit；and the optimization is a new approach to analyzing of underground structure reliability.
