Abstract: As single-phase earth fault occurs in the small current grounding system, the complex transient and unconspicuous steady-state component of fault current bring certain difficulties for reliable fault line selection. The transient component characteristics of fault current in the small current grounding system are analyzed and a method about fault line selection based on improved EMD algorithm is put forward in this paper. The method of solving the IMF modal aliasing problems by overlaying the characteristic high frequency signal in EMD algorithm also reliable filter high frequency noise. It can be used in different fault time. In view of IMF which get by the improved EMD algorithm under different fault angle show different characteristics, the low frequency waveform monotonicity in the fault time and the fault characteristic energy can be used to determine the fault line. At last the effectiveness of the proposed fault line selection methods is verified by the simulation results of the single-phase earth fault in distribution network built in Matlab/Simulink.