In order to ensure the reliability and continuity of the cabinet of mobile substation grounding, and guarantee the safety of the equipment and workers, ground wire should be monitored, so the new cable ground wire monitoring protection equipment is proposed. Through comparing and analyzing the possible single-phase fault, ground break fault and short-circuit fault, it is found that both the three fault signals and the normal signals have obvious characteristics, based on which the reliable criterion can be established. In the actual running, the equipment can test the single-phase fault, the ground break fault and short-circuit fault and do the right action, so the fault judgment criterion used in the equipment is effective and practical, which can ensure a reliable ground.