The method for detecting single-phase grounding fault based on the harmonic component of residual current is provided, in which collecting and calculating the phase differences of third harmonic waves relative to the fundamental wave of the residual current in the feeder line, and judging if the phase differences of the residual current in the feeder line is into a threshold range, and judging if there is a suspected grounding fault, and confirming the fault event by judging the duration and the generated times of the suspected grounding fault. Another method for detecting single-phase grounding fault based on the harmonic component of residual current is provided, in which the residual current of neutral point is used.