The invention discloses a method for determining a reverse current at a protective installation place upon faults occurred to a series compensated line. The method analyzes electrical features of a series compensated line through the selection of through a transition resistor earth fault at feature fault points of the series compensated line, and determines features of the reverse current of the series compensated line. The method comprises the following steps: firstly determining fault attributes of the series compensated line (metal or transition resistor earthing), and if the metal earth fault is determined, then a series compensated apparatus must be bypassed, and the reverse current is not considered; and if a through a transition resistor is determined, then comparison is needed between a system value-equivalent resistance (referred as a system resistance) behind the protective installation point of the series compensated apparatus and an effect-equivalent resistance (referred as a series compensated resistance) of the series compensated apparatus, and if the system resistance is greater than the series compensated resistance, the reverse current is not considered; and if the system resistance is smaller than the series compensated resistance, then the reverse current features are determined based on the features of the series compensated resistance changes upon through a transition resistor earth fault occurred to different fault positions in combination with motions of a metal oxide varistor (MOV). The invention provides a method for determining a reverse current in a series compensated line.