To　investigate　the　characteristics　of　offshore　ground　motions,　981　ground　motion　records　recorded　by　5　offshore　stations　and　6　onshore　stations　in　124　seismic　events　were　selected　based　on　the　K-NET　network　in　Japan.　The　typical　ground　motion　parameters,　dynamic　amplification　coefficient　spectra,　and　vertical-to-horizontal　response　spectral　ratio　were　analyzed　after　data　screening　and　ground　motion　data　processing.　The　results　show　that　the　weakening　of　vertical　ground　motion　by　seawater　causes　the　vertical　peak　acceleration　and　duration　to　be　significantly　smaller　than　the　horizontal.　The　seabed　site　conditions　have　an　amplifying　effect　on　offshore　ground　motions,　then　the　selection　of　onshore　ground　motions　for　seismic　design　of　marine　engineering　will　underestimate　the　impact　of　seismic　loads.When　the　period　0.1s＜T＜0.8s,　the　dynamic　amplification　factor　spectra　of　offshore　ground　motion　is　larger　than　that　of　onshore　ground　motion.　And　the　maximum　value　of　the　dynamic　amplification　factor　spectra　of　offshore　ground　motion　is　larger　than　the　values　of　the　seismic　design　code　spectra,　and　it　is　risky　to　use　the　existing　seismic　design　code　to　start　the　offshore　construction.　©　2023　Science　and　Technology　Periodical　Press.　All　rights　reserved.