The invention discloses a power transformer DC magnetic bias restraining method. The power transformer has three phase inputs and three phase outputs, the power transformer is formed by three primary windings and three secondary windings, third windings are wound on a common iron core of the power transformer and serve as DC compensating windings, the third windings are connected in series with a DC current source controlled by the current, a DC current transformer is installed on a neutral point of the primary windings, three third windings are arranged and are connected in series with one another, and the polarity of the current output by the DC current source is opposite to that of DC through the neutral point of the primary windings of the power transformer. According to the invention, transformer DC magnetic bias is restrained by starting with the internal structure of the transformer body, the cost is relatively low, power transformer DC magnetic bias restraining method has good feasibility, reliability and practicality, and good DC magnetic bias restraining effect can be achieved.