Abstract: Aiming to address the issue of the existing traveling wave distance measurement being influenced by frequency variation of wave velocity and time error, a combined fault location method for DC grid transmission lines is proposed based on time difference characteristics of traveling waves. Firstly, the basic principle of fault location is clarified by analyzing the time difference characteristics of the initial backward traveling wave, so as to determine the objective function and construct the original fault location model. Subsequently, the model undergoes two refinements by considering the frequency variation of wave velocity, time error and the results of traditional double-terminal traveling wave ranging method. The virtual fault distance, wave velocity and time errors are then optimized by particle swarm algorithm to achieve accurate fault location. Finally, the effectiveness of the proposed ranging method is verified by digital simulation. A large number of simulation results demonstrate a significant improvement in accuracy and the ability to achieve full-line fault location compared with the traditional double-terminal traveling wave method. It remains unaffected by fault location and exhibits strong resistance to transition resistance (500Ω). Additionally, it also has low requirements for data synchronization and sampling frequency.