The invention discloses a system for reducing potential of a subway train track. The system for reducing the potential of the subway train track comprises a return line, a negative impedence converterand a switch unit which is used for connecting the return line with a running rail. The system for reducing the potential of the subway train track is applied to the existing subway rail transit direct current traction power supply system; by adjusting output impedance of the negative impedence converter, the impedance from a return point of a traction substation to a closed switch unit via the negative impedence converter and the return line is enabled to approach zero and then the current of a train on the running rail in this section is transferred to the return line so that the potentialof the closed switch unit approaches the potential of the return point of the traction substation. According to the system for reducing the potential of the subway train track, the track potential inthe existing system can be greatly reduced to greatly reduce stray current corrosion. The system for reducing the potential of the subway train track can also be used for reducing the track potentialof a track in a novel direct current traction power supply system based on direct current auto-transformer power supply or can be used for reducing the track potential of a track in an alternating current traction power supply system.