Abstract: In case of insulation breakdown accident of ultra-high voltage (UHV) gas insulated metal-enclosed transmission line (GIL), the accurate location of breakdown position is conducive to emergency repair and rapid recovery of power transmission. This paper proposes a fault location method based on transient voltage monitoring for UHV GIL, which is actually applied in 1 100 kV Sutong GIL utility tunnel project. The system includes voltage sensor, monitoring terminal, and storage and control unit, which are successfully installed and implemented. During GIL field tests, when the GIL flashover occurs, the system successfully triggers and completely records the transient voltages generated during the breakdown. Through waveform analysis, it is found that when UHV GIL solid insulation breaks down, the half-wave steepening time of transient voltage is less than 130 ns and spreads between the breakdown point and bushing port, forming a typical traveling wave process. According to the time when the transient traveling wave first reaches the measuring points at both ends of GIL, combined with the propagation speed of traveling wave, the accurate position of the fault point is calculated and the fault point is quickly disassembled for maintenance. According to the results of disintegration verification, the positioning error of the system is less than 5 meters. It can be seen that the adoption of wide-band voltage sensing based on capacitive voltage divider can realize the rapid and accurate location of insulation breakdown faults of UHV GIL, which is conducive to improving the operation reliability of UHV transmission system.