The low frequency signal injection method is one of the DC system grounding fault detection methods. The detection accuracy is high and easy to operate. But it also easy to be impacted by the large amount of ground capacitance. To avoid this interference, this text raise a method combined the data extraction based on coiflet wavelet transform and the data processing base on multi-target optimization. This method decrease the affect by the ground capacitance. With the simulation verification in matlab, the result prove the method has increase the accuracy in DC system grounding fault detection indeed.