Abstract: In order to obtain the hoop water inflow of the undersea tunnel,the pore water pressure distribution behind the undersea tunnel lining is taken as the key factor,a prediction formula relating to pore water pressure is then derived,employing Darcy’s law as the basis.This formula takes into account the tunnel’s dimensions and the permeability coefficient of the tunnel lining,while also thoroughly incorporating the influence of water pressure behind the supporting structure.Subsequently,water inflow values for each part of the tunnel are computed and compared against field data to validate the formula’s accuracy.The results show that the influence range of seepage field caused by tunnel excavation in FLAC3D is concentrated in three times diameter of the tunnel,and the main influence range is concentrated in two times diameter around the tunnel.During excavation,the seepage field around the tunnel presents a funnel-shaped distribution until the excavation is completed.The lower the surrounding rock quality,the higher the pore water pressure behind the tunnel lining.The pore water pressure at the invert typically surpasses that at the arch,and the maximum pore water pressure generally occurs at the junction between the side wall and the invert.By comparing the water inflow calculated by prediction formula with the actual situation of the field,the accuracy of the formula is confirmed.The water inflow prediction formula has certain guiding significance for the water inflow prediction during the construction of the undersea tunnel.