The invention discloses a full-wave overvoltage protection method for a high-voltage transmission line. The method comprises the following steps: S1, collecting the full-wave voltage of the high-voltage transmission line; S2, extracting the harmonic component and the fundamental component in the full-wave voltage; 3, setting a harmonic overvoltage starting value and performing start protection when that harmonic voltage meets the starting condition; S4: calculating the harmonic content ratio of the full-wave voltage; S5: tripping and signaling are effected by judging the harmonic content ratio, the rms value of the fundamental component, and the instantaneous value overvoltage. The voltage sampling frequency of the full-wave voltage of the high-voltage transmission line collected in the step S1 is 3600 Hz. The extracted harmonic component in the step S2 is a second to seventh harmonic voltage in the full-wave voltage; Considering that the harmonic overvoltage in the power network is mainly the second to seventh harmonic voltage, and the harmonic voltage content above the seventh harmonic voltage is very low, the harmonic components extracted are the second to seventh harmonic voltages of the full-wave voltages.