Abstract: The DC system of the substation is mainly responsible for supplying power to all the remote communication circuits, protection circuits, control circuits and emergency lighting in the station. When the DC system fails, it will cause the protection or automatic device to refuse or misoperate, which will bring great hidden dangers to the safe and stable operation of the power grid. This paper takes the DC ring network fault caused by the three-phase inconsistent circuit distribution error of a 220kV substation circuit breaker as an example, firstly analyzes the basic theory of ring network fault. This paper expounds the harm and principle of the grounding fault of the ring network, focuses on the treatment process of the DC ring network fault, and finally summarizes the treatment of the DC ring network fault and puts forward improvement measures, which provides a certain reference for the protection personnel to deal with the DC-related fault.