The high development of HVDC makes a contribution to the transformer DC magnetic bias, which does harm to power system and the transformer itself seriously. Therefore it is necessary to restrain the current in the neutral line. the commonly methods used to restrain DC magnetic bias are connecting a resistor or a capacitor in the neutral line and so on. The paper proposed a suppression method based on DC electric potential compensation after comparing the traditional methods. In addition, presented a novel topology of a device based on the method above. What is more, ran the simulation models with PSCAD/ EMTDC, and conducted experiments in the lab, whose results are in accordance with each other and prove that the topology has a satisfying performance on restraining the neutral current.