Abstract: Aiming at the problem that the stray currents leaked during the operation of the urban subway have caused the DC bias of the transformers along the line, a DC bias suppression method based on the SiC PiN diode is proposed in this paper. First, a stray current distribution model is established and the ground potential data are measured and collected, which clarifies the numerical distribution characteristics of the whole earth potential in the downtown area during the subway operation. Then, based on the voltage blocking ability and the current conduction characteristics of the SiC PiN diode at the DC voltage and the fault current, the structure and working flow of the DC bias suppression circuit for the transformer based on the SiC PiN diode are presented. Finally, based on the PSCAD/EMTDC simulation platform, the DC bias simulation model of the main transformer in the 110kV substation of the urban power grid is established to verify the fault current conduction ability and the effect of the DC bias suppression. The simulation results show that the DC bias suppression instantaneously conducts when the power grid is faulty with the relay protection quickly act in tripping; After the transformer applies the DC bias suppression, the neutral DC current is blocked, the distortion rates of hysteresis loop, the primary winding current and the excitation current are reduced, and the DC bias is effectively suppressed.