Present situation of underground power supply system was introduced in this paper, reasons of non selective tripping error were analyzed when override trip and leakage fault occurred and some solutions were put forward. Based on override tripping in short circuit fault, a new scheme of sampling, processing and output of intelligent integrated protection of underground explosion - proof switch was put forward as the backup protection which provided an direct current quick - break protection scheme. In this paper, a scheme of different protection modes for total feed switch and branch feed switch was proposed for the non selective tripping of the leakage fault. The actual operation showed that modified BGP series of high-voltage explosion-proof switch effectively avoided large-scale power outage caused by the leap-off, reduced security risks and improved production efficiency.