The　heavy-duty　mechanical　spindle　is　a　key　functionalcomponent　of　the　milling　head　of　heavycomputer　numerical　control(CNC)　machine　tool,　which　is　used　for　processing　the　large　andcomplex　parts　with　free-form　surface.　The　spindle　has　the　characteristics　of　high　torque　and　high　power.　The　accuracy　of　finite　element　modeling　and　modal　analysis　of　the　spindle　are　the　basis　of　further　dynamic　analysis　of　spindle.　The　kinetic　equation　of　heavy-duty　mechanical　spindle　is　established　based　on　Timoshenko　beam　theory,　and　dynamic　equations　of　spindle　in　matrix　form　are　gained　by　finite　element　method.　Spindle　is　meshed　by　solid　element　and　beam　element　respectively　in　finite　element　software,　and　bearing　is　meshed　bycombin14　spring　element.　The　modal　analysis　of　heavy-duty　mechanical　spindle　is　performed　in　the　boundary　of　free　and　actual　constraints.　Radial　stiffness　of　bearing　is　calculated　based　on　bearing　type,　which　is　the　stiffness　parameter　of　spring　element　in　spindle　modal　analysis.　Modal　experiment　of　spindle　by　hammer　exciting　is　performed,　and　experiment　results　agree　well　with　the　simulated　results　of　spindle　under　multiple　constraints.　The　research　results　show　that　the　Timoshenko　beam　and　Beam188　are　more　accurate　and　the　case　of　beam　constrained　by　spring　is　according　with　the　reality　for　the　heavy-duty　spindle　modeling.　The　results　provide　basis　for　further　optimization　design　and　precision　control　of　heavy-duty　mechanical　spindle　system.　©　2012　Journal　of　Mechanical　Engineering.