Traveling wave travels between fault point and the end of line for a lot, forming natural frequencies which have mathematical relationship with fault distance. Smoothing reactor and DC filter constitute the boundary of UHVDC, making the natural frequencies more clear. Based on these, a UHVDC transmission line pilot protection method based on features of dominant components of natural frequencies is put forward. Changing ratio is used to form fault start principle; MUSIC method is used to conduct a spectral analysis of the transient current after fault, and the difference between dominant components of natural frequencies of internal fault and external fault is used to form protection principle; the dominant components extracted by formal signals and modal signals are used to form fault line principle, forming the whole protection scheme. UHVDC model is established in PSCAD/EMTDC and lots of simulations on different fault conditions are done on this model. Lots of simulations show that this method can work precisely and quickly under different fault conditions, and has good adaptability and practical values.