Based on the transient traveling wave generated by the fault of the transmission line, which can meet the requirement in terms of speed for high speed transmission lines in quick response to the protective devices, and can achieve an accurate location of the faults without being affected by the fault type. The main factors influencing the accuracy of traveling wave fault are the speed of traveling wave and the calibration of the arrival time of the traveling wave heads. In view of the commonly used methods for determining the wave speed of lines：formula method and online measurement method, the corresponding traveling wave velocity can be obtained by simulation analysis at different line lengths and different fault distances. The obtained wave velocity is used for the same fault distance measurement. A comparison and analysis made of the ranging results helps to determine the optimal wave velocity at some fault distance, thus improving its ranging accuracy. A simulation analysis shows that the accuracy of the on-line real-time measurement of the wave velocity is higher than that of the fixed wave velocity in appropriate ranges, which meets the requirement of the standard deviation within 1%.