Theeffectsoftheconstantexcitationonthelocalbifurcationoftheperiodicsolutionsinthe1:2internalresonantsystemswereanalyzedbasedonthesingularitytheory.Itisshownthattheconstantexcitationmakeinfluenceonlywhenthereexistsomenonlinearterms,intheoscillatorwithlowerfrequency.Besidesactingasmainbifurcationparameter,theconstantexcitation,togetherwithcoefficientsofsomenonlinearterms,maychangethevaluesofunfoldingparametersandthetypeofthebifurcation.Underthenon-degeneratecases,theeffectofthethirdordertermscanbeneglected.
