This work proposes a novel UHF RFID axle counting system and conformal tag antenna applied in this system. The axle counting system consists of the tag reader, the reference tag antenna, and the tag antenna on the surface of the trains. When the train passes the axle counting system, the tag reader can detect the tag antennas. The system calculates and records the number of axles and judges whether the train has passed through an intersection. Furthermore, the proposed tag antennas on the system are conformal tag antennas with impedance transformers based on parallel coupled lines. The working frequency of the designed tag antenna is 920 MHz, with a gain greater than 5.4 dBi. The tag antenna prototypes are fabricated using additive manufacturing techniques. The measurement results show that the designed tag antenna has sufficient communication distance, and great potential in train safety detection combined with the proposed axle counting system.