For　the　nonlinear　disturbance　actual　issues　of　the　model　space　drive　mechanism　two-stage　spur　gear　system,　a　nonlinear　dynamic　model　of　14-DOF　(degree　of　freedom)　two-stage　spur　gear　with　time-varying　stiffness　and　damping　was　established.　This　model　has　been　developed　previously　by　the　authors　to　access　the　large　inertia　on　the　dynamic　response　of　spur　gear　space　drivingmechanism,　and　its　effectiveness　was　proved　by　a　motion　simulation　experiment.　In　this　paper,　the　profile　error　(PE)　and　the　index　error　(IE)　were　enhanced　in　the　dynamic　model.　The　effects　of　profile　error,　index　error,　and　variable　load　torque　on　transmission　error　(TE)　were　analyzed,　while　the　optimization　was　proposed　according　to　the　analyzed　result.　The　peak-to-peak　value　of　the　optimized　load　transmission　error　(LTE)　was　reduced　by　60.7%,　which　improved　the　transmission　accuracy　and　reduced　the　phenomenon　of　disturbance.　The　research　of　nonlinear　dynamical　model　of　two-stage　spur　gear　and　the　TE　of　the　large　inertia　load　were　enriched,　which　provided　an　important　reference　for　the　actual　design　of　the　gear　system.