The invention discloses a method for measuring the overvoltage of a power transmission line. It is assumed that the line overvoltage of an nth base tower of a certain power transmission line needs tobe measured, the method comprises the steps that the nth base tower is provided with a recorder used for recording the voltage waveform, one end of the recorder is connected to an overhead ground lineinsulated from the tower body, and the other end is connected to the tower body; the recorder is provided with a trigger threshold, and does not record the voltage waveform when the line operates normally; when the line has overvoltage, the overhead ground line couples the induction voltage, and the recorder is triggered and records the voltage waveform; a coupling coefficient between the overhead ground line and the line is calculated according to an electromagnetic field theory, and the overvoltage on the line is calculated according to the voltage waveform and the coupling coefficient. According to the method, the measurement for the line overvoltage at the middle of the power transmission line can be achieved; there is a certain distance between the overhead ground line and the line,and the coupling voltage of the overhead ground line is low, so that measurement equipment can be miniaturized, the power consumption is reduced, and all-weather real-time monitoring can be realized;and the measurement is carried out in a full-automatic manner, and no manual operation is required to be performed.