The identification rate of fault line for single-phase earth fault in resonant grounding system is normally low due to the weak fault current signal by the arc suppression coil. This paper proposes a new method to detect the fault line in resonant grounding systems based on the characteristics of the low similarity between zero-sequence current waveform through fault line and the one through non-fault line. First, the HHT(Hilbert-Huang transform) method and time-spectrum band-pass filtering method are used to process the zero-sequence current waveform. Then, the time-frequency energy matrix of the zero-sequence current waveform through each line is constructed. Finally, the detection of the fault line is realized by combining the similarity recognition method in image recognition with comprehensive similarity coefficient matrix. Simulation results illustrate that the proposed fault line detection method is effective and reliable for noise interference and two-point grounding fault in resonant grounding systems.