Abstract: The advantages and disadvantages of the traveling wave protection of HVDC transmission line are summarized, and proposed the problems in the raveling wave protection, as well as faulty analysis method for these problems at the same time, which is starting from the frequency domain transmission system, deep analyze the transient component propagation of the DC transmission line that mainly including the characteristics of frequency-dependent parameters of the DC line and the border composition by filter system. Thence the effective band between outside and inside fault of the line is proposed. The analytical methods could provide a reference value for DC circuit transient protection.