In order to solve the problem that the fault line cannot be accurately identified after single-phase grounding fault occurs in power grid,an intelligent sensing method of residual current grounding fault based on wavelet packet decomposition was proposed.Based on wavelet analysis and intelligent sensing principle,the residual current generated by grounding fault was collected,and the collected residual current information was analyzed and compared to sense the grounding fault and identify the fault.By researching on-line monitoring of residual current of AC power supply and arc grounding fault diagnosis technology which is based on wavelet transform,the time-frequency characteristics of current obtained by wavelet packet decomposition were used for fault line selection;the fault line selection method based on the proposed wavelet packet decomposition was simulated.The results show that the time-frequency information can be extracted accurately and the fault line can be determined effectively by using the method,and the fault line can be accurately identified with the difference of current characteristics between fault line and normal line.The research result provides a reference for the design of intelligent sensing system of AC power grounding fault.