With development over time, the immersed tunnel is becoming increasingly important. This tunnel is generally built in underwater environments and requires special considerations with respect to its design and safety factors. Researchers around the globe have conducted many studies on this type of structure and have found that it can be affected by the liquefaction of the foundation and hydrodynamic pressure due to earthquake, the interaction between soils and structures, and the oblique incidence of seismic waves. In this paper, we use the time-domain wave method coupled with a viscous-spring artificial boundary condition and the equivalent stress input method to obtain the oblique incidence of shear-vertical (SV) waves. The half-space numerical results demonstrate this method to have good precision. We then applied the proposed method to investigate the seismic response of the Haihe immersed tunnel subjected to the oblique incidence of seismic waves. The simulation results show that the dynamic responses of the immersed tunnel subjected to the action of obliquely incident seismic waves clearly differ from those due to vertically incident seismic SV waves. With increases in the incident angle, the stress on the immersed tunnel increases, and a larger stress point appears in the four corners of the tunnel and in the connection between the partition wall and the bottom plate and the roof, with the middle partition wall being the weakest point. With increases in the incident angle, the relative maximum horizontal displacements of the side wall and partition wall increase, and the displacement of the middle partition wall is the greatest. With increases in the incident angle, the vertical acceleration rate of the tunnel structure increases significantly. Therefore, seismic research of immersed tunnel structures should consider the effect of obliquely incident seismic waves.