Abstract: Describes the fault overview of the backup protection of the No.1 main transformer in the 110 kV Bakeshenying station prior to the protection action of 313 line of Barker line, analyzes the action of No.1 main transformer and the protection action of 313 line of Barker line. The starting information of the 314 protection of Balao line is added to the overall fault analysis. Since the line protection is not accurate, the fault recording waveform and the internal waveform of the line protection are unified by using the fault characteristics of three-phase current mutation and zero sequence voltage, the whole fault situation is restored. It is concluded that the 313 protection of No.1 main transformer and Barker line are correct.