By virtue of the good property of frequency division of wavelet packets， the phase currents of feeders of a distribution network with a single phase to ground fault， are decomposed to obtain the outputs of different frequency bands. The feature frequency band of each line， in which the distribution of the transient current of the healthy phase is most concentrated， is adaptively chosen according to the view of maximum energy. The state of each line is judged with the ratio of the energy of the faulty phase to the energy of the healthy phase. Simulation in PSCAD and analysis in MATLAB prove that this scheme can distinguish the faulty feeder from the healthy feeder correctly with higher sensitiveness.