The　rigid-structure　method,　Morison　method　and　a　method　based　on　approximation　of　fundamental　frequency　are　applicable　simplified　methods　for　the　hydrodynamic　force　of　incompressible　non-viscous　water.　To　investigate　the　differences　of　the　above　methods,the　responsesof　elastic　cantilever　circular　piers　were　compared　in　the　form　of　frequency　domain　transfer　function,　with　the　exact　solutions　which　based　on　the　radiation　theory　of　incompressible　non-viscous　water　considering　structural　deformation.　Two　kinds　of　size　parameters　were　selected　and　84　different　sizes　of　piers　were　designed.　By　inputting　impulse　excitation,　the　transfer　functions　of　displacement　at　the　bottom,　the　transfer　function　of　shear　force　and　bending　moment　at　the　top　were　obtained.　Then　the　first　two　order　resonance-peak　amplitude　and　resonance　frequency　were　extracted　for　error　analysis.　Through　the　analysis　of　the　range　and　variation　trend　of　errors,　it　is　found　that:　the　resonance　peak　amplitude　obtained　by　the　rigid-structure　method　is　more　accurate,　the　resonance　period　obtained　by　the　method　based　on　approximation　of　fundamental-frequency　is　more　accurate,　and　the　error　of　the　Morison　method　is　significantly　affected　by　the　parameters.　In　addition,　the　amplitude　of　formant　obtained　by　the　fundamental　frequency　approximation　is　mostly　smaller,　while　the　amplitude　and　period　obtained　by　the　Morrison　method　are　mostly　larger.　©　2020,　Engineering　Mechanics　Press.　All　right　reserved.