In　this　study,　multi-pulse　chaotic　dynamics　of　an　unbalanced　Jeffcott　rotor　with　gravity　effect　are　investigated.　Based　on　the　solvability　conditions　obtained　for　the　case　of　one-to-one　internal　resonance　and　primary　resonance,　canonical　transformations　are　used　to　reduce　these　ordinary　differential　equations　to　a　standard　form　suitable　for　applying　the　energy-phase　method.　The　global　perturbation　technique　is　employed　to　demonstrate　the　existence　of　chaotic　dynamics　by　identifying　multi-pulse　jumping　orbits　in　the　perturbed　phase　space.　The　chaotic　dynamics　results　from　the　existence　of　ilnikov＇s　type　of　homoclinic　orbits　and　the　parameter　set　for　which　the　system　may　exhibit　chaotic　motions　in　the　sense　of　Smale　horseshoes　are　obtained　analytically.　The　global　solutions　are　then　interpreted　in　terms　of　the　physical　motion　of　the　rotor　system,　and　the　dynamical　mechanism　of　pattern　conversion　between　the　localized　mode　and　the　coupled　mode　is　revealed.