Abstract: The analysis of seismic response at seabed sites is a crucial initial step in marine engineering construction. In this study， a fluid-solid weak coupling model is employed to replicate the interaction between seawater and the seabed. Specifically， four representative borehole sections along the proposed tunnel at Qiongzhou strait are chosen to investigate the influence induced by seawater， soft sediments， and bedrock earthquake motion on the seismic responses of the seabed site. A generalized non-Masing constitutive model （DCZ model） is utilized to account for the dynamic nonlinearity of the seabed soft soil. The findings indicate that the suppression effect of seawater on seismic motion in the seabed is limited to depths shallower than 50 m. Furthermore， the suppression effect is more pronounced in the vertical direction compared to the horizontal direction. Additionally， there is a positive correlation between the suppression effect of seawater on seismic motion at the seabed surface and the frequency response phenomenon characterized by high frequency suppression and low frequency amplification in the seabed seismic response. This correlation is influenced by the depth of the seawater. The mean lines of the horizontal and vertical spectrum β obtained by numerical calculation are higher than the design spectrum in the land code in several period ranges， and the possibility of adverse effects induced by seawater and seabed soft sedimentation on the seismic resistance of marine structures should be considered.