Single phase-to-ground fault often occurs in a distribution network with its neutral point usually insulated or compensated with a coil. Processing and classification of such fault data can help expedite diagnosis and restoration to normal network condition. This paper proposes a method for classifying the phase-to-ground fault in terms of its waveform characteristics using the phase-plane method. The fault data are first characterized by the discrete points in the phase-plane domain with the phase-plane divided into three areas. Then the characteristic vector of the fault data is established by counting the percentage of discrete points in each area of the phase-plane. The hierarchical cluster algorithm is adopted to implement the classification of the fault data according to the average distance between classes. A group of field recorded fault data is classified， showing that the results obtained using the proposed method are rational and accurate.