Due to the uncertainty of traveling wave velocity and the influence of transmission line sag,the existing traveling wave fault location methods are p rone to large positioning errors.Therefore,a traveling wave fault location met hod is proposed,which does not need the setting of wave speed and line length. The traveling wave signal detection device at both ends of the line is used to r ecord the arrival time of the fault voltage traveling wave head.At the same tim e,according to the propagation path of the voltage traveling wave in the proces s of refraction and reflection,the equations about distance,speed and time are listed.After mathematical transformation,the influence of the line sag can be eliminated,and the traveling wave speed can be measured on line in real time. The PSCAD software is used to simulate the transmission line with two terminal s tructure.The experimental results show that the method has good adaptability.I n the actual location,it has low dependence on the electrical parameters of the line,and is not affected by the fault type,fault location and transition resi stance.The positioning error is small,the principle is simple,and it has high accuracy and good applicability.