This paper focuses on the stray capacitance of HVDC key devices and its impact on the harmonic distribution and the problem of obtaining wide band models for electrical power system transient simulation purposes for EMTP with linear components. Smoothing reactor, converter transformer and the valve hall can be modeled with stray parameters by segmented wide-band model with skin effect resistance. The simulation curve of the model can already be consistent with measured curves, and it can reflect the resonance characteristics in low frequency and fit the stray capacitance well in high frequency. The analysis of overvoltage fault proves that the stray capacitance played an important role in fault analysis with respect to harmonics distribution of HVDC system and the model with stray parameters has significant value of application.