Most long-distance transmission lines of 1000 km or above in China adopt ultra-high-voltage direct current (UHVDC) transmission, and their configured main and backup protections basically meet the requirements for selective fault clearance. However, high-resistance faults still rely on backup protection with higher delays, which not only reduces the speed but also undermines the power angle stability of parallel systems. To address these issues, this paper proposes a novel protection based on the arrival time difference of frequency-divided traveling waves. First, a theoretical analysis of the dispersion characteristics of traveling waves on UHVDC lines is conducted by studying the wave speed and attenuation characteristics of traveling waves at different frequencies, which are quantified using predominance and time difference indicators. Second, the wavelet packet transform is utilized to extract the high/low-frequency bands of aerial mode traveling waves, with transient extraction transform employed to restore the reduced time-domain resolution due to the use of such a frequency-band division transform. Finally, a novel protection for the LCC-UHVDC is proposed according to the dispersion characteristics of the aerial mode wave that quantified by the transient extraction transform. Simulation studies demonstrate that the proposed protection can identify internal faults within 1 ms, covering more than 95% of the line length, and possesses a resistive tolerance of over 600 ohms.