Abstract：Considering the sea water seepage，limit analysis by finite element method is used to study the stability of a subsea tunnel in which the fracture zone exists. Result shows that the tunnel is safe for the intact surrounding rock. Under the condition，the lining of the subsea tunnel can be designed without water pressure；and the lining thickness can be reduced remarkably. The calculation results show that the fault-rupture zone decreases the stability of tunnel obviously. The wider the fracture zone is，the smaller the safety factor is. The thicker the rock grouting ring is，the larger the safety factor is. Slip surface of intact surrounding rock appears at both sides of tunnel；and the stability of rock mass in fracture zone with angle of 45°is the most unfavorable. So the pregrouting treatment is necessary in order to cut down the seepage water. Under this condition，the tunnel lining can be designed according to principle with water pressure.
