Traveling wave protection is widely used as the main protection in DC lines. However, as a single-ended protection, traveling wave protection has the disadvantages of high maloperation and poor resistance to transition resistance. Based on the analysis of the propagation characteristics of traveling wave in DC transmission system, according to the different change directions of transient current traveling wave in internal and external faults, a longitudinal directional protection based on the transient current traveling wave mutation for LCC-MMC hybrid bipolar DC transmission system is proposed in this paper. If the mutation directions of transient current traveling waves on both sides are the same during the fault, it is an internal fault, otherwise it is an external fault. The simulation results of PSCAD and MATLAB show that the protection can quickly and accurately identify the faults under different fault types, different fault resistances and different fault location distance, so it has certain practicability.