The invention relates to a rail transit signal system which is used for realizing bidirectional communication between a ground region control center and on-vehicle ATP and ATO equipment, in particularto a symmetric induction loop bidirectional communication system. The system comprises a loop line cable, on-vehicle equipment and ground equipment. The loop line cable is symmetrically paved along the center of two steel rails; crossing points are arranged at every distance; the ground equipment comprises transmitting equipment and receiving equipment which are respectively connected with the region control center by buses; a coupling transformer is arranged between the transmitting equipment and the receiving equipment; and the output of the coupling transformer is connected to a beginningmatching device of the loop line cable through a feeder cable. The system uses a transformer-coupled circuit so that signal transmission distance is doubled; and via coupling counteracting, after thesignal which is received by the transformer-coupled circuit and returned from the loop line passes through a filter circuit, a ground-to-vehicle signal is substantially filtered and the signal to noise ratio of a vehicle-to-ground signal is greatly improved.