The invention relates to the technical field of power devices, in particular to an insulator arc-over locating system used in a GIS voltage withstanding process. The insulator arc-over locating system comprises a data acquisition unit, data processing units (3), data transmission units (4) and a data display unit (5). According to the locating system, due to the fact that two kinds of data acquisition modes are adopted, and independent circuits are designed, the circuits have the remarkable advantages that the circuits have the same function, supplement each other and do not restrict each other; the system can locate the failure point in advance according to a partial discharge signal and stop continuous boosting operation, and damage to devices is avoided; the failure point can be located precisely, failure point processing is made to have pertinence, processing efficiency is improved, time in power transmission is shortened; due to the fact that wireless transmission is adopted, the trouble that multiple wires are connected at site can be saved, working efficiency is improved, and an operator can observe the detection result at any time through a display; furthermore, ultrasonic transducers are adopted, partial discharge signal can be detected effectively, external disturbance is lowered, and the failure position can be judged in advance; high-speed processors are adopted, and data accuracy can be improved remarkably.