Due to the hysteresis effect, there will be residual magnetism in the iron core of the transformer after the circuit breaker is opened. When the circuit is closed again, if the closing angle is not appropriate, the residual magnetism will cause the iron core to enter the saturation region, causing excitation inrush current, which poses a threat to the stability of equipment and power grid. In order to effectively address this issue, a reliable method for suppressing excitation inrush current of transformers is needed. Therefore, this paper proposes a method to suppress excitation inrush current of power transformers. This method first demagnetizes the transformer, eliminating the unknown residual magnetic flux inside the transformer to 0. Then, a magnetizing device is used to set the three-phase magnetic flux of the transformer to meet the conditions for phase selection and closing of the transformer, achieving suppression of excitation inrush current. Finally, simulation results show that this method can further reduce excitation inrush current, proving its effectiveness.