In order to prevent the damages of stray currents, the mass rapid transit (MRT) system has electrical insulation between the MRT depot and the main line tracks, however, the potential difference of different grounding systems is the most important factor of electrical corrosion on tracks. When steel wheels of train stride over two different grounding systems, they momently short the different potentials, and produce an electrical arc that causes track corrosion. Therefore track corrosion is closely related to the track-to-ground potential and the return current of train. For reducing corrosion on insulating rail joint (IRJ) in depot boundary of the mass rapid transit system, this study makes the following three suggestions: (1) Don't receive and/or dispatch train when the rails of depot area are in solid ground situation. (2)Don't receive and/or dispatch train when the track-to-ground potential of main line is too high. (3)Increase track-to-ground resistance in depot area.