The invention discloses an auxiliary positioning system of urban rail transit train under a fault environment, including an RFID information tag module, an RFID reader, an infrared emitter and an infrared sensor. By using RFID technology, the vehicles in the traveling section are located, which not only can the position information, the traveling speed and the traveling direction of the train be detected when the train is traveling, but also the traveling acceleration of the train can be deduced after the train passes through, and the dynamic running state of the train can be judged more accurately, thus ensuring the safety of the line transportation and realizing the safety interval control of the train. At that same time, the infrared induction technology and the RFID technology are adopt to jointly complete the parking position operation. Under the condition of signal system failure, the train can transmit the information to the staff in time, reduce the influence and loss caused bysignal system failure, make the train stop and enter the station more accurately, and meet the actual requirements of the rail transit enterprises for positioning equipment layout.