In this paper, traveling wave (TW) propagation velocity on HVDC systems is assessed. Most TW-based fault location methods consider that all wavefronts travel throughout transmission lines at the same velocity. However, TW velocities change according to various factors, such as fault distance and line electrical parameters. In HVDC systems with long lengths, these velocities may significantly vary, leading the premise of equal velocities over the line to be no longer valid. To assess the TW propagation velocity on HVDC grids, controlled fault cases are carried out by means of Alternative Transients Program (ATP) simulations in a CIGRE benchmark model, which represents the Madeira River HVDC Bipolar System. The obtained results show that the TW velocities are affected by the fault distance, decreasing as they travel along the line. Moreover, it is demonstrated that the higher the soil resistivity, the lower the TW propagation velocity.