In　order　to　simulation　the　vibration　characteristics　of　the　transmission　system　of　the　rolling　mill　in　Engineering.　To　determine　the　cause　of　the　door　threshold　of　rolling　mill　vibration　damage,　source　the　vibration　of　rolling　mill.　This　article　from　the　perspective　of　multi　body　dynamics,　Use　the　rigid　flexible　coupling　dynamic　model,　fully　considered　of　the　time-varying　mesh　stiffness　of　the　gears,　backlash,　speed　and　other　factors.　Simulation　the　vibration　characteristics　of　the　transmission　system　of　the　rolling　mill　in　different　tooth　side　clearance　and　different　speed.　The　result　show　that,　with　the　increasing　of　the　backlash,　the　vibration　amplitude　of　the　output　shaft　increase　first　and　then　decrease　and　then　increase.　Motion　state　by　no　impact　to　unilateral　shock,　bilateral　impact　and　then　enters　to　a　chaotic　state　finally　to　no　impact.　Through　dynamics　simulation,　can　draw　the　vibration　characteristics　in　different　tooth　side　clearance　and　different　speed　of　the　transmission　system　of　the　rolling　mill,　the　theory　basis　for　the　fault　diagnosis　of　the　transmission　system　of　the　rolling　mill.　©　(2014)　Trans　Tech　Publications,　Switzerland.