The lossless transmission line model is widely used in research of propagation characteristic of fault traveling wave on HVDC line, but traveling wave dispersion is not considered in the model. And the influence of DC line terminal devices is not considered in research of traveling wave protection (TWP). The causation, the characteristic and the influencing factors of fault traveling wave dispersion are analyzed in detail. Influence of DC line terminal devices on the reflection of different frequency component of fault traveling wave is also analyzed. And then, influence of the forenamed two factors on TWP is studied. It is shown that dispersion mainly affects the earth mode component of fault traveling wave. Both the forenamed two factors also have effect on the amplitude of fault traveling wave, which affects the criterion of voltage change of TWP; the fault traveling wave gradient, which affects the criterion of voltage change rate of TWP, is affected limitedly by dispersion. And it can be confirmed by the aerial mode component of fault traveling wave.