Traditional DC-side active harmonic method has the problems of complex circuit structure and great power losses. This paper suggests an active harmonic suppression technique on the DC side to enhance the harmonic suppression capabilities of the input side of the series 12-pulse rectifier. This method uses an inverter circuit with a center-tapped transformer to generate a square wave voltage and inject it into the DC side, adjust the output current of the rectifier, and then adjust the rectifier's input current so that it closely resembles a sine wave based on the relationships between the DC side's injection voltage and the AC side's current flow. The analysis and simulation structure show that when the load changes, the grid-side current's overall harmonic distortion rate is below 3.5%, and this strategy can effectively suppress the harmonics of the rectifier input current.