The invention relates to a method for decoupling a transient voltage measurement waveform by three-phase steady-state voltage information, and belongs to the technical field of the overvoltage measurement of the electric transmission line of a power system. The method comprises the following steps that: independently placing three electric field sensors below a three-phase alternating current electric transmission line to be measured; when the electric transmission line carries steady-state voltage, independently measuring steady-state electric field waveforms as E1, E2 and E3 by a sensor 1, asensor 2 and a sensor 3; constructing a decoupling matrix, and solving the decoupling matrix M; obtaining an inverse number from the decoupling matrix M to obtain a decoupling matrix M-1; and utilizing the decoupling matrix M-1and electric field waveforms Ea, Eb and Ec to solve a decoupled practical transient voltage signal. By use of the voltage decoupling method which is put forward by the invention, the voltage waveform on each phase of circuit can be obtained.