In order to suppress the DC magnetic bias caused by transformer neutral point DC effectively, this paper proposes a novel reverse DC injection device based on high-frequency switching power supply, and introduces the structure and working principle of device in detail. This object uses the modular high-frequency switching power as the injected source, and takes advantage of PLC to monitor and control the system, so the device not only can react the magnetic bias rapidly and accurately but realize the real-time monitoring and compensate the transformer neutral point DC. After simulation test and field operation, the result shows that the device does well in balancing transformer neutral point current, and guarantees the current stay in the preset range. So the reliable performance of device can meet the actual needs of the project.