Abstract: By analyzing a hidden case of DC opposite pole series connection in a 500kV substation, this article describes the abnormal phenomenon of DC opposite pole series connection between the operating power supply and the remote signaling power supply in detail. It provides a method for dismantling the cable cores on the positive and common terminals of the remote signaling power supply one by one and monitoring whether the operating power supply"s ground voltage disappears. The reasons for the occurrence of DC opposite pole series connection are analyzed. A method of pulling circuit breakers has been proposed for technical renovation and new expansion projects to verify the independence of each DC circuit and prevent the occurrence of DC crossover defects.