Accurate transmission line fault location is of great practical significance for improving the efficiency of fault treatment and guaranteeing the reliability of a UHVDC system. A fault location strategy for a DC transmission line based on an improved D-type twin-terminal traveling wave method is designed. First, the derivative method is adopted to accurately judge the range of fault occurrence time. Then, the exact time when the traveling wave reaches both ends of the line is determined by wavelet modulus maximum analysis. Based on the first and second moments when the fault traveling wave reaches the measuring end, an improved D-type two-terminal traveling wave ranging method is designed. It eliminates the influence of traveling wave velocity on fault ranging. The simulation results show that the error of fault ranging is small. It indicates that the improved D-type two-terminal traveling wave method has higher fault location accuracy. At the same time, it has good adaptability to different types of faults and different transition resistances, and can also be applied to the location of near-area faults. This work is supported by National Natural Science Foundation of China (No. 51477120).