Abstract: As the traditional research show,the resonance of the traction network happens when the characteristic spectrums of the AC drive electric locomotive or the EMUs match or are close to the resonant frequency.However,the resonance caused by the non-characteristic spectrum is measured many times in the actual operation.Based on the characteristic of the locomotive current under the transient current control strategy,the mathematical expression of the time varying cyclic effect of the train net coupling in the harmonic environment was given.This paper analyzed such a interaction process that the severely distorted net voltage caused by the resonance of the high-order harmonics acts on the PWM modulation of the rectifier of the locomotive and the locomotive output current,in turn,the locomotive output current acts on the net voltage.As a result,the main spectrum distribution of the locomotive current will move with the variation of the different resonance points of the traction net.Based on the simulation and measured data,the theoretical analysis was verified by the phenomenon of the main order of the locomotive current spectrum moves to the resonant frequency of the traction network.