The　effect　of　hydrodynamic　force　on　the　seismic　response　of　structure　in　water　cannot　be　ignored.　Various　methods　have　been　developed　to　describe　the　effect　of　incompressible　water,　but　the　relative　performance　of　some　practical　simplified　methods　is　largely　unknown.　In　this　paper　a　comprehensive　comparison　of　three　representative　simplified　methods　for　assessing　cylindrical　hydrodynamic　force　is　presented.　Relative　errors　of　structural　elastic　peak　responses　are　constructed　to　measure　the　accuracy　of　the　simplified　method.　The　errors　are　tested　on　154　circular　cylinders　subjected　to　100　ground　motions.　The　errors　were　first　obtained　by　averaging　the　results　of　ground　motions.　Then　the　comparison　between　methods　and　the　influence　of　parameters　were　studied　based　on　the　mean　errors.　Furthermore,　by　analyzing　the　statistical　characteristic　values　of　the　errors,　the　kernel　density　estimation　method　was　adopted　to　obtain　the　probability　density　of　the　errors.　Finally,　the　probabilities　of　cylindrical　cases　and　methods　were　investigated.　The　results　show　that　if　the　added　mass　of　hydrodynamic　force　depends　on　more　structural　parameters,　the　accuracy　of　the　method　may　higher.　The　rigid-structure　method　has　the　highest　accuracy　and　the　most　complicated　expression.　The　accuracy　and　complexity　of　the　method　based　on　approximation　of　fundamental　frequency　are　moderate.　The　Morison　method　has　the　simplest　form　and　the　maximum　error.　The　results　indicate　that　the　added　mass　should　relate　to　several　structural　parameters,　ignoring　the　change　of　the　added　mass　along　the　height　will　bring　error　to　method　and　assuming　the　structure　to　be　rigid　is　an　effective　way　to　simplify　the　analytical　hydrodynamics.