When HVDC transmission lines fault, the high frequency transient signal travels along the lines, and the high frequency component attenuates during the course. The phase-model transform is analyzed, the frequency characteristic of double-poles UHVDC transmission lines is studied, and the conclusion that the UHVDC transmission lines attenuate the high frequency component, the UHVDC transmission line is longer, the attenuation is acuter is drawn. The single-ended fault location theory of UHVDC transmission line based on high frequency attenuation characteristic is studied, the distance calculation formula of fault position is deduced, and the conclusion that the single-ended fault location theory of UHVDC transmission line based on high frequency attenuation characteristic can not realize the fault location exactly is drawn. The double-ended fault location theory of UHVDC transmission line based on high frequency attenuation characteristic is studied, the distance calculation formula of fault position is deduced, the conception of frequency band attenuation is put forward, the distance calculation formula of fault position based on frequency band attenuation is deduced. The actual parameter simulation model of Yunnan-Guangdong UHVDC system is built up, and the double-ended fault location theory based on high frequency attenuation characteristic studied in this paper is simulated and the simulation location result is higher accurate.