During　the　operation　of　the　planetary　gear　box,　the　vibration　signal　comes　mainly　from　the　meshing　vibration　between　the　gears.　The　position　between　each　meshing　point　and　the　sensor　changes　periodically,　and　each　meshing　vibration　signal　was　collected　by　the　sensor　through　different　transmission　paths　at　the　same　time,　resulting　in　serious　coupling　of　the　signal　collected　by　the　sensor　and　very　complicated,　which　is　not　conducive　to　effective　failure　diagnosis.　To　this　end,　considering　the　actual　characteristics　of　signal　acquisition,　a　rigid-flexible　coupled　dynamic　simulation　model　was　established　by　using　PROE,　ANSYS　and　dynamic　simulation　software　ADAMS　according　to　the　laboratory　equipment　parameters.　Combining　with　the　time-varying　dynamics　model　proposed　by　Inalpolat,　and　considering　the　local　fault　signal　modulation,　rotational　modulation,　the　structure　and　constraint　modulation　of　each　gear　of　the　gearbox,　an　improved　time-varying　dynamics　model　of　local　fault　was　established.　By　comparing　the　results　of　the　improved　local　fault　time-varying　dynamic　model　and　the　simulation　model,　the　characteristics　of　amplitude　and　side-frequency　spacing　in　the　planetary　gearbox　sideband　signal　were　obtained,　which　verifies　the　consistency　of　the　model　and　theory.　Finally,　compared　with　the　experimental　signal,　the　correctness　of　the　conclusion　was　verified.　The　result　of　this　study　can　provide　an　effective　theory　and　engineering　basis　for　planetary　gearbox　fault　diagnosis.　©　2019,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.