In this paper, the mechanism of harmonic overvoltage resulting from exciting inrush current is analyzed, and it is found that its essential reason is the combined action of standing-wave effect and the resonance effect on the transmission line. Moreover, the limitations of existing suppression methods, such as phase selection switch and closing resistor, are also analyzed: phase selection switch requires the breaker switching time to be less than 1ms, which could be very difficult due to achieve due to the discreteness of the breaker and the transformer residual magnetism in reality; on the other hand, if transformer residual magnetism is considered, the switching of the closing resistor cannot suppress the exciting currents of all phases because of its switching time. Therefore, under the condition that the direction of transformer residual magnetism is known, a comprehensive suppression method of exciting inrush current is proposed in this paper, which optimizes phase selection and closing resistor switching. Simulation was carried out on a certain regional power grid in Sichuan, and results indicate that the proposed suppression method is effective and has some robustness under different operating conditions.