Offshore　structures　in　zones　of　active　seismicity　are　under　a　potential　threat　caused　by　the　combined　action　of　earthquakes　and　waves.　Taking　a　submerged　circular　cylinder　as　the　prototype　and　considering　water-structure-soil　interaction,　the　present　study　is　devoted　to　the　investigation　of　the　combined　action　of　earthquakes　and　waves.　Water-cylinder　interaction　and　soil-structure　interaction　are　simulated　by　added　mass　and　rigid　circular　massless　foundations,　respectively.　Based　on　the　radiation　and　diffraction　wave　theory,　the　scaled　boundary　finite　element　method　is　utilized　to　determine　the　earthquake-induced　and　wave-induced　pressure　on　a　circular　cylinder.　Then,　a　closed-form　expression　for　the　natural　frequencies　and　mode　shapes　of　the　system　is　derived　by　using　the　transfer　matrix　method,　where　the　transfer　matrix　is　obtained　based　on　Euler-Bernoulli＇s　beam　differential　equation.　Furthermore,　the　dynamic　response　of　the　system　under　the　combined　action　of　earthquakes　and　waves　is　derived　by　using　the　mode　superposition　method.　Finally,　the　effects　of　the　hydrodynamic　force,　wave　force,　and　soil-structure　interaction　on　the　dynamic　response　of　the　submerged　cylinder　are　investigated.　The　results　indicate　that　the　wave　forces　can　substantially　increase　the　dynamic　responses　of　the　cylinder　and　that　the　influence　increases　as　the　stiffness　ratio　increases　and　the　width-depth　ratio　decreases.　It　is　necessary　to　consider　the　combined　action　of　earthquakes　and　waves　in　the　seismic　design　of　offshore　structures.