Abstract: There is no special code for seismic design of immersed tunnels in China at present. Furthermore, inertia of the tunnel, complex ground conditions, non-uniform seismic excitation at the bottom of the tunnel and dependence of soil-structure interaction coefficient on earthquake excitation frequency are always neglected in the past analysis methods for seismic response of immersed tunnels. Based on this consideration, a frequency-domain analysis method for longitudinal seismic response of immersed tunnels is established using the Winkler foundation-beam theory and the fast Fourier transform technique. The response displacement method and frequency-domain analysis method based on Winkler foundation-beam theory are used to compute Hong Kong-Zhuhai-Macao (HZM) immersed tunnel, and difference between the two approaches is discussed. Some conclusions and suggestions are presented for the seismic design of HZM immersed tunnel. Although this research is prompted by need of a concrete project, the proposed methods are universal and can be applied to the analysis and design of other immersed tunneling projects.