The current UHVDC transmission lines mainly adopt traveling wave fault location method, but the single/double terminal traveling wave fault location is affected by the velocity and the transmission line sag effect, thereby such fault location has low accuracy. Based on the moment of the opposite terminal traveling wave arriving at the measuring terminal of location device, the influence of traveling wave velocity is eliminated through the formula derivation and single terminal fault location method for UHVDC transmission line is deduced which is not affected by wave velocity and can realize fault location without accurately calculating the velocity along the line. The model of Ha-Zheng ±800 kV UHVDC transmission system is built in PSCAD/EMTDC and simulated under different fault locations and different transition resistances. A large number of simulation results show that the improved single terminal ranging method is not affected by the wave speed along the transmission line and the location of the fault, and has the strong ability to tolerate transient resistance. This work is supported by Joint Natural Science Foundation of the Xinjiang Uygur Autonomous Region (No. 2017D01C028).