Overheating　faults　of　gas-insulated　bus　(GIB)　plug-in　connectors　induced　by　contact　degradation　seriously　threaten　the　safe　operation　of　equipment　and　power　system.　Multiphysics　coupled　numerical　simulations　and　physical　experiments　were　conducted　in　this　article　to　reveal　contact　degradation　processes　of　the　GIB　plug-in　connector.　First,　electromagnetic-thermal-mechanical　coupled　finite-element　(FE)　model　was　built.　Relative　motion　between　contact　interfaces　was　considered　by　low-velocity　Stribeck　friction　model.　FE　model　was　verified　by　physical　experiment.　Second,　influences　of　operation　current,　spring　stiffness,　and　conductor　insert　depth　on　contact　temperature　rise　were　analyzed.　Results　show　that　insufficient　conductor　could　induce　overheating　on　several　contact　spots　then　accelerate　the　degradation　process.　Third,　thermal　and　motion　characteristics　under　cyclic　operation　currents　and　short-circuit　(SC)　current　impact　were　analyzed.　Results　show　that　conductor　insert　depth　could　be　changed　by　relative　motion　between　contact　elements.　Relative　motion　accumulates　gradually　under　cyclic　thermal　loading　by　operation　current.　Significant　relative　motion　and　temperature　rise　could　be　induced　by　SC　current　impact.　Finally,　progressive　and　sudden　failure　mechanisms　of　the　GIB　plug-in　connector　were　discussed.　Research　result　may　guide　optimal　design　and　field　maintenance　of　GIB　equipment,　and　thus　improves　its　reliability.