Offshore　structures　in　earthquake-prone　areas　are　threatened　by　seismic　and　wave　currents.　The　dynamic　response　of　a　cross-sea　bridge　with　rectangular　pier　under　the　action　of　earthquake　and　wave　is　analyzed　in　this　paper.　Firstly,　the　main　girder　structure　and　pier　structure　of　the　sea-crossing　bridge　are　discretized　as　Euler　beam　element　and　fiber　element　(nonlinear)　by　finite　element　method,　respectively.　Moreover,　the　waterstructure　interaction　is　replaced　by　additional　mass,　and　the　soil-structure　interaction　is　replaced　by　horizontal　spring,　horizontal　damping,　rotating　spring　and　rotating　damping.　After　that,　based　on　the　analysis　of　the　natural　vibration　frequency　of　the　structure,　the　influence　of　the　interaction　between　the　water-structure　and　the　soil-structure　stiffness　on　the　natural　vibration　frequency　of　the　structure　is　discussed.　The　effects　of　structure　nonlinearity,　soil　foundation　spring,　soil　foundation　damping,　hydrodynamic　pressure,　travelling　wave　and　wave　force　on　sea-crossing　bridge　are　studied　based　on　dynamic　response　analysis.