An extraction approach of fault superimposed components in an evolved fault is proposed. Based on the superimposed theory of linear systems， a fault power system can be broken down into a normal system network and a fault superimposed system network. This approach firstly calculates fault superimposed components before the evolved fault occurred at the measuring point. Then by subtracting the calculated currents fault superimposed components from the currents of the moment at the measuring point， load currents in the normal system network is obtained. After an evolved fault occurred， the fault superimposed components can be calculated through subtracting the solved load currents from the currents at the measuring point. The proposed approach is free of influences of load and network parameters， etc. The digital simulation in the IEEE 9-bus system model verifies the applicability of the approach.