Abstract: Application of grounding current online monitoring technology in traction power supply is few, and monitoring effect cannot be evaluated. The improved cable grounding current online monitoring system was applied to traction power supply system to verify the operating effect of grounding current online monitoring technology.Through judgment and validation of anomalous circulating current, it was clear that the existing criteria of power system for grounding current could not be directly applied to traction power supply system, and preliminary decision characteristics were presented. At the same time, by comparing load current and grounding current on both sides of traction substation, it was found that load current of traction cable could affect load current of supply cable in traction substation. Therefore, it was necessary to strengthen the monitoring of supply cables in traction substation.