Based on the transient zero-sequence characteristics, this paper studies the zero-sequence transient characteristics of low current grounding system in frequency domain. Starting from the characteristic variable of zero-sequence impedance at the line inlet which changes with frequency, this paper deeply excavates the impedance characteristics of zero-sequence impedance of each feeder in the distribution network system, discusses the variation law of amplitude and phase angle of zero-sequence impedance with frequency in detail, and analyzes different neutral grounding modes and whether the line is sound or not, so as to make better use of zero-sequence transient signal and improve fault diagnosis The correct rate of detection lays a solid foundation. Finally, a simulation model is built by PSCAD to verify the characteristics.