In order to research the harmonic resonance characteristics of the traction network, an equivalent harmonic circuit model of train-catenary integrated system is established based on the Thevenin harmonic voltage source model, and the mechanism of the traction network resonance over-voltage is analyzed based on the principle of the impedance voltage divider. The simulation study of the harmonic resonance characteristics of the traction network and the phenomenon of the traction network resonance over-voltage is made based on Matlab/Simulink. The simulation results show that the content of the roof grid voltage harmonics is very large when the frequency of greater content of the locomotive converter AC side voltage harmonic coincides with the frequency of the traction network resonance point, which cause the traction network resonance over-voltage, and the traction network resonance over-voltage can be suppressed by changing the carrier frequency of the locomotive converter and the length of the power arm. This work is supported by Fundamental Research Funds for the Central Universities (No. 2015JBM085).