Abstract: DC transmission, especially modular multilevel converter-based high voltage direct current（MMC-HVDC）transmission, raised high demand for high speed operation of relay. When a fault occurred, the fault traveling wave contained of wide-band frequencies was generated and transmitted to both ends of the transmission line. Due to the frequency-dependent characteristics of the transmission line parameters, the distorted traveling wave front at the end of the transmission line contained fault information. In this paper, the fault information contained in traveling wave front was analyzed.Using the relationships between 1) the traveling wave front distortion and the fault distance, 2) the traveling wave front amplitude and the fault resistance, the generalized logistic function was constructed to extract the fault distance/resistance by fitting the wave front of zero-mode fault current. Then a novel high speed protection principle for DC transmission was proposed using the fitting coefficient. The simulation results show that the proposed principle is fast and can correctly act even with high fault resistance.