The invention relates to the field of power system protection and controlling, and provides a voltage travelling wave differential protection method in which a line parameter frequency variation characteristic is considered. The method can ensure higher accuracy and higher speed in detecting faults in an area. The technical solution of the voltage travelling wave differential protection method ofthe flexible DC power transmission line is characterized in that the influence of a flexible DC line frequency related parameter is considered; a characteristic impedance and a propagation coefficientof a frequency-related power transmission line are calculated in the time domain; through acquiring voltage signals and current signals at the head end and the tail end of the power transmission line, forward voltage travelling waves and backward voltage travelling waves at the head end and the tail end of the power transmission line are respectively calculated; and furthermore through comparingthe difference between the head-end voltage travelling wave and the tail-end voltage travelling voltage with a preset voltage threshold valve, whether a fault occurs in an area is determined. The method is mainly applied to the occasion of power system protection and controlling.