In this paper, the seismic response of underwater shield tunnel to incident P waves is investigated by using the Fourier-Bessel series expansion method. On the basis of the exact analytical solution, it is studied that the seismic response of the system which is made up of tunnel lining structure, underwater soil and water. The influence that water depth and buried depth of shield tunnel put on the seismic response of tunnel lining is given. The analytical result shows that the seismic response of tunnel lining unobvious varies with water depth change when incident P waves have a small incident angle, nevertheless, opposite conclusion appears when oblique incident P waves have a big incident angle. At a certain incident angle, the seismic response of tunnel increases with the increasing of the water depth; and the seismic response decreases with the increasing of the buried depth of underwater tunnel.