Abstract: In order to investigate the bearing behaviors of surrounding rock and lining of tunnels under external water pressure, the numerical simulation based on the stochastic finite element method (SFEM) is conducted to analyze the behaviors of Longtan tunnel. In SFEM, the response surface method (RSM) and the Monte-Carlo method are adopted. In the analysis, the following calculations are made: i) fitting responsive surface equation, ii) analysis on probability sensitivities and correlations. It is shown that the failure mode of the lining under external water pressure is mainly compressive failure; the increase of the elastic modulus of surrounding rock is more effective than that of the lining. Based on the analysis, in lining design and tunnel construction under external water pressure, the following factors should be considered the bearing characteristics of surrounding rock, the calculation model of layer structure method and the grouting effects including water plugging and reinforcement.