Abstract: The judgement logic of Xi′an Metro Line 3 traction system overvoltage and overcurrent is introduced. By analyzing data of TCMS (train control and management system), it is concluded that the traction system detects coasting when the train is operating on the main line, which leads to motor phase current overcurrent and DC filter voltage overvoltage, triggering temporary protection state of traction system, and tripping off high-speed circuit breaker. The detailed description of the traction system control strategy and coasting control strategy are expounded, and optimization and improvement measures are proposed.