Abstract: By means of deduction of zero-sequence current expressions when single-phase grounding fault occurs in single substation mode and multi-substation mode of coal mine resonant grounding system, polarity relationship between transient pulse of fault line and normal line, and relationships among amplitude or width of transient pulse, grounding resistance, shunt capacitance and fault time were analyzed, and corresponding expressions were given. Polarity of transient pulse of fault line is opposite to the ones of normal lines, and amplitude of the transient pulse of fault line is the largest among all lines. The amplitude of transient pulse at the fault time is inversely proportional to grounding resistance and proportional to sin of angle of fault phase. All the normal lines have the same width of transient pulse, which is smaller than the one of the fault line, and the width of transient pulse is proportional to the grounding resistance. The Matlab/Simulink simulation proves correctness of above theoretical conclusions.