Abstract: The harmonic current generated by electric locomotives will penetrate into the public power grid,resulting in voltage distortion at the Point of Common Coupling (PCC).In order to study the harmonic penetration characteristics of the bilateral power supply system,the chain circuit model of the traction network is established based on the parallel multi-conductor transmission line theory;the harmonic model of electric locomotive is established based on the measured data.On this basis,the harmonic power flow calculation method of the bilateral power supply system is given.The harmonic penetration characteristics and its influencing factors of the bilateral power supply system are analyzed by calculating and evaluating the total harmonic distortion of the voltage at PCC.The results show that the total harmonic distortion of the voltage at the PCC is reduced for bilateral power supply compared to unilateral power supply.The larger the short-circuit capacity of the external power supply,the smaller the total harmonic distortion of voltage at