Abstract: Objective: Chongqing monorail vehicles are equipped with GR (carbody grounding relay), power supply system is equipped with 64D (grounding leakage protection device). When the grounding leakage fault occurs in either of them, the operation will be interrupted, resulting in greater impact. Studying their interaction mechanism allows efficient identification of grounding leakage fault causes, locating the faulty points and assisting in resuming operation. Method: By analyzing the action mechanisms of both monorail vehicle GR and of power supply system 64D, their interactive relation and influence during grounding leakage are identified; the grounding leakage fault cases of Chongqing monorail Line 2 are reviewed. Result & Conclusion: According to the time, situation and sequential happenings during power supply system and vehicle grounding leakage faults are analyzed, a list for judgment and treatment of failure vehicles is formulated. Through practical application, it is proved that the faulty points can be quickly located to solve the problem.