The　electro-hydraulic　servo　steering　system　is　one　of　the　core　components　of　a　heavy　vehicle,　and　frequency　response　characteristics　of　this　system　are　essential　to　guarantee　the　vehicle　flexibility.　However,　it　is　difficult　to　establish　frequency　domain　model　directly　for　the　frequency　response　characteristics　analysis　due　to　the　strong　nonlinearity　of　steering　trapezoidal　mechanism　and　hydraulic　power　system　in　electro-hydraulic　servo　steering　system.　This　paper　proposes　a　simplified　linearization　analysis　method　for　the　electro-hydraulic　servo　steering　system.　By　variable　substitution　defining　the　load　flow　and　load　pressure,　and　linear　fit　between　double　tire　angles　and　cylinder　displacement,　the　original　model　is　simplified　to　a　frequency　domain　model.　Based　on　this　model,　the　essential　frequency　response　characteristics　and　the　effects　of　key　parameters　to　electro-hydraulic　servo　steering　system　can　be　obtained.　Through　the　sweep　frequency　response　analysis,　the　linearized　frequency　domain　model　is　compared　with　the　nonlinear　time　domain　model　and　the　actual　test　system,　respectively.　As　shown　in　Bode　plots,　the　amplitude-frequency　phase-frequency　characteristic　curves　of　models　match　well,　which　verifies　linearization　analysis　method　and　linear　frequency　domain　model.　The　key　parameters　affecting　the　system　frequency　domain　characteristics　are　the　valve　flow　gain,　the　area　of　cylinder　rodless　and　rod　chamber,　and　the　linearization　coefficient　between　the　left　and　right　tire　angles　and　so　on.　The　electro-hydraulic　servo　steering　system　bandwidth　is　only　7.38　rad/s　(1.17　Hz).　This　research　is　helpful　for　the　design　and　optimization　of　heavy　vehicle　dynamic　steering　system.　©　IMechE　2020.