Abstract: To study the effects of seepage and earthquakes on a subsea tunnel structure, a subsea tunnel passing through a fracture zone was selected to be studied. The surrounding rock was defined as a continuous porous medium. Considering the visco-elastic artificial boundary and fluid-solid action between the surrounding rock and pore water, the finite element software ADINA was used to analyze the variation of pore water pressure in the tunnel surrounding rock during horizontal seismic action, the effects of hydrodynamic pressure in a porous medium on the tunnel lining and the effects of the combined action of a porous medium seepage field and seismic stress field on tunnel safety and stability. The numerical calculations show that the effects of hydrodynamic pressure in a porous rock medium on the structural internal force of a tunnel during seepage is significant and must be addressed. Additionally, the stresses and strains at the spandrel, the springing, and both sides of the tunnel lining increase dramatically under seismic action.