Abstract：Xiamen East Passage subsea tunnel is the first subsea tunnel with large cross-section in China，and its geological conditions are complex and unfavorable with enriched groundwater. The deformation of tunnel support in the entrance of Xiang¢an part is great. To reinforce the surrounding rock and reduce the effects of groundwater，the constructor dewaters the water level with wells based on in-situ experiences of similar engineering. To ascertain the effect of dewatering with wells，the parameters of wall rock by field experiment，i.e. disassemble experiment，shear experiment，are gained；and then，the construction safety was calculated with numerical analysis. Finally，the effects of the dewatering wells were achieved with the results of numerical analysis and locally measured data. The effects are mainly shown as follows：the arch-crown settlement of tunnel will be decreased to 50%，that of and horizontal convergence will be decreased to 30% after considering the dewatering wells；meanwhile，the range of plastic area also will be reduced to large extent，and the tunnel support safety will be increased.
