High-frequency transient current component is used to select fault line in indirectly grounding power system, but the frequency range is usually chosen by experience method. In the view of this situation, this paper analytically analyses the frequency characteristics, proposes a method to estimate the frequency range, provides the feature components between fault line and non-fault line and lays the theoretical foundations for high-frequency component selecting. On the basis of frequency analysis, this paper extracts high-frequency components in the selected frequency range by using the existing filtering tool, calculates the relative entropy coefficient matrix combined with the relative entropy theory and then identifies the fault line. Simulation results show that the proposed route selection method has wide applicability and accuracy.