In order to determine the harmonic distribution and propagation characteristics of traction system in high-speed railway, this paper proposes a novel harmonic load-flow method based on the multi-transimission model of traction network and harmonic load model of high-speed train(CRH2). The coupling relationship between traction network and high-speed train are fully considered, i.e. coupling between harmonic voltage of traction lines and harmonic injection currents of the train. This harmonic load flow method is applied to analyze the harmonic distortions of the whole system when single train and multiple trains run on the track. The results indicate that the proposed method is suitable for harmonic load flow in traction system with single or multiple harmonic sources and background harmonics. Moreover, this method can provide reference for analyzing and controlling of harmonic resonance in traction system since it performs well in reflecting the harmonic resonance phenomenon.