Abstract: For low accuracy and poor adaptability of the existing macro-fault line selection method in the practical application of distribution network,based on an in-depth analysis of the transient characteristics of ground faults in the resonant grounded distribution network,this paper proposes a new method of inner product transformation fault line selection based on micro-characteristic quantity measurement. First,the fault characteristic mode is obtained by using the modal decomposition algorithm,and the singular value points of the fault are obtained based on the first-order difference of the characteristic mode. Second,the inner product transformation line selection criterion is constructed at the singular value point of the fault,and then the comprehensive inner product value that reflects the fault characteristics of each feeder is obtained.Finally,the difference between the maximum inner product value and the minimum inner product value is compared with the preset threshold value,so as to judge whether it is feeder fault or bus fault. Simulation results show that the proposed method is simple in principle and has high accuracy in line selection,and can adapt to most fault conditions.