The groundwater problem in underground engineering is an important issue influencing the stability of subway tunnel.Based on the coupled fluid-mechanical theory

the finite difference method of fast Lagrangian analysis of continua is applied to analyze the fields of displacement

stress

and pore- pressure in the surrounding soils of an excavated tunnel under various conditions of groundwater levels

different depth of the tunnel.It can be concluded from the numerical simulation of excavation that the groundwater flow have an obvious effects on the distributions of displacement

stress and pore-pressure in the surrounding soil.The seepage forces of groundwater will increase the displacement in the soil around the tunnel and the stress in the tunnel linings.According to the basic deformation compatibility condition of surrounding soils and supporting structure of tunnels

the necessity of considering the seepage effect of ground water in design of tunnel excavation and its supporting structures has been proved in this paper to demonstrate the important effects of groundwater on the stability of tunnels.