Abstract: The problem of DC bias seriously threatens the safe operation of ultra-high voltage transformers, especially under conditions of geomagnetic storms and harmonic interference. This article proposes a three-level suppression technology scheme of "source suppression propagation blocking influence weakening" to address the problem of DC bias. The focus is on designing harmonic current compensation devices, impedance optimization equipment, and magnetic flux compensation systems, and the effectiveness of the technology is verified through experiments. The research results indicate that this scheme can significantly reduce the harm of DC bias to transformers, providing effective guarantees for the safe operation of ultra-high voltage transformers.