Abstract: To solve the problem that faulty trains can't be accurately identified when the DC traction power supply system for the dedicated return rail has a short circuit fault between the positive pole and the train, a precise identification method is proposed for fault trains based on train grounding current. Firstly, an equivalent model is established for the bilateral power supply traction system. Secondly, the difference of train grounding current characteristics between the faulty trains and the normal trains are analyzed. Finally the precise identification method for fault trains based on the train grounding current is proposed. The proposed method uses the amplitude and direction of the train grounding current as the fault identification criteria. The train is judged as normal when the amplitude of the train grounding current is less than the setting value; the direction of the train grounding current is used as criterion when the amplitude is greater than or equal to the setting value, and the train with positive current direction is judged as faulty and the train with opposite current direction is judged as normal. This method is simple in principle and easy to implement. The adoption of bi-criterion can effectively avoid misjudgment and improve the reliability. The feasibility and effectiveness of the proposed method are verified by Matlab simulation and field test.