Abstract: Aiming at the problems of many parts of the trackless trolley auxiliary transportation system and mutual interference of electric leakage detection and incorrect positioning, the AC-DC power supply and distribution system, overhead contact network and wired electric vehicle leakage detection method were proposed respectively by analyzing the circuit components and structure of each subsystem. And a kind of direct current contact line leakage detection scheme which is several kilometers in length was introduced emphatically. The results showed that exchange high and low voltage circuits using selective leakage protection, rectifier feed-back circuit using differential current leakage protection, contact network circuit using the compensation switching bridge leakage protection, and the wired vehicle using secondary insulation and bus insulation test can achieve leakage grading power protection and reduce the fault range.