Abstract: Based on the traditional flexible DC transmission line traveling wave protection, there are problems of insufficient resistance to transition resistance and lack of basis for protection setting. This paper firstly analyzes the attenuation characteristics of the initial traveling wave frequency components of fault protection installations inside and outside the area, and reveals the attenuation law of the initial traveling wave frequency components of faults in the area and the difference between the initial traveling wave frequency components attenuation of the faults inside and outside the area. Then, the initial traveling wave analytical formula of the fault at the protection installation is deeply analyzed, the influence of the high frequency component in the energy calculation is enhanced, and the main frequency component of the initial traveling wave that can reflect the fault location and the attenuation characteristics of the line boundary is constructed. The analytical formula of the main frequency component of the initial traveling wave shows that the main frequency component decreases with the increase of the fault distance, and there is a significant difference between the main frequency component of the initial traveling wave inside and outside the fault. On this basis, a single-ended traveling wave protection method based on the attenuation characteristics of the initial traveling wave main frequency component is proposed. This method makes full use of the full frequency band information of the initial traveling wave. The component analytical formula also provides a theoretical basis for the protection threshold setting. The simulation results show that the protection scheme proposed in this paper can quickly and accurately identify the internal and external faults, the main frequency component of the initial traveling wave can effectively reflect the fault location, the setting is simple and easy, the ability to withstand transition resistance is strong, and it has better performance under different network topologies with Strong adaptability.