For common grounding electrode, if one of the lines is being maintained and another is under mono-polar earth operation, operating current will flow into the ground and be picked up partly by tower at overhaul side, which will finally flow into the grounding grid of converter station through lines and affect the equipments and personal safety in converter station. In this paper, personal safety risks such as stepping voltage and touch voltage caused by the current flowing into the grid of converter station during the line maintenance of Yulongling common grounding electrode are calculated and analyzed, and DC bias of transformers in converter station is evaluated with the power system grouding analysis software CDEGS under monopole grounding operating mode with rated current. Results show that the current flowing into the grounding grid during the line maintenance are unable to cause personal safety risks but may result in the excess of transformers bias current in Suidong converter station.