The utility model discloses a portable DC grounding system fault locator, which comprises an ultralow-frequency signal generator, wherein the ultralow-frequency signal is connected with a protective circuit, and is connected with a processor through an ultralow-frequency signal receiver, the processor is connected with a nixie display and an alarm, and the processor is further connected with a detection device. The portable DC grounding system fault locator can completely eliminate the grounding faults of DC systems and the interference of field distributed large capacitor, and can accurately lock the faults within a minimum range.