Abstract: Under the action of an earthquake, a sea tunnel is subjected to hydrodynamic pressure, so it is of great significance to study the dynamic response of sea tunnel under the combined action of earthquake and hydrodynamic pressure. Based on Biot’s theory of dynamic consolidation and elastodynamics theory, this paper established a mechanical model of tunnel-soil-fluid interaction by considering the two-phase property of seabed （soil） and the viscoelastic artificial boundary and the action of fluid （water）-structure interaction, and then discussed how the tunnel and its surrounding seabed are affected by the condition with or without water, and the depth of water, the buried depth of the tunnel, the nature of the seabed soil and change of incident angle. The results show that: ① the pore water pressure of the seabed soil and the internal stress of the tunnel increase with water depth increasing; ② different seismic wave and seabed soil characteristics have a great impact on the internal stress of the tunnel and the pore water pressure; ③ the permeability of seabed soil and the depth of the tunnel have a small effect on the internal stress of the tunnel, whereas it has a great effect on the pore water pressure of the seabed soil; ④ the incident angle of the seismic wave has a great influence on the internal stress of the tunnel and the pore water pressure of the seabed soil.