Large　inertia　load　has　been　widely　used　in　space　driving　mechanisms,　but　the　research　concerning　theory　is　still　an　unexplored　scientific　field.　Towards　the　problem　of　nonlinear　disturbance　in　space　driving　mechanism　with　large　inertia　load,　a　14-DOF　(Degree　of　Freedom)　nonlinear,　time-varying,　dynamic　model　of　two-stage　spur　gear　system　was　established,　taking　into　consideration　time-varying　stiffness,　backlash　and　transmission　error.　The　dynamic　response　of　the　load,　under　large　or　small　inertia　was　investigated,　basing　on　the　dynamic　model.　The　results　indicate　that　at　starting,　normal　operation　and　braking,　large　inertia　load　system　has　obvious　hysteresis,　compared　to　small　inertia.　The　factors　that　improve　dynamic　response　speed　under　large　inertia　load　were　studied.　The　results　indicate　that　improving　the　stiffness　and　damping　of　the　output　shaft　and　changing　the　material　of　second　gear　pair　to　titanium　alloy　are　helpful　in　improving　the　dynamic　response　speed　of　the　system.　Some　results　enrich　the　research　of　two-stage　spur　gear　nonlinear　model　and　large　inertia　load,　since　they　provide　important　reference　for　the　actual　design　of　the　gear　system.　©　JVE　INTERNATIONAL　LTD.