To solve the lack of common methods of ground fault detection method, this paper proposes a new double balance bridge detection method for DC system circuit grounding fault detection. In this method, the programmable controller switches twice resistance switching, and then monitoring unbalance current in the double balance bridge and the branch leakage current, calculating the ground fault resistance and positioning the grounding branch. This paper first expounds the basic principle and application of double bridge detection, and then proposes a new double balance bridge detection method to solve the problem of detection of dead zone and this detection method is not affected by the influence of distributed capacitance. Finally, through experiments proved the feasibility and effectiveness of this method.