In order to analyze the cause of bars breaking of squirrel-rotor by intermediate frequency induction brazing of traction motor of a certain locomotive,fracture microstructure has been analyzed by electron microscopy scanning macro metallography. The fracture site stress distribution under different contact modes between rotor core punch and bars,and the influence of natural frequency on bars of the rotor has been analyzed by finite element software. The bars breaking preventive measures of the repaired motor and the improvement scheme of the new motor has been put forward to solve the questions,which has solved the breaking of rotor,and ensured the safety of the locomotive operation.