Abstract: In response to the prominent low-order harmonics and insufficient coordination of external filtering in the operation of high-power variable-frequency equipment in wastewater treatment plants, taking an industrial wastewater treatment plant as an example, the harmonic characteristics of main loads such as aeration fans and lift pumps were analyzed, and an integrated design scheme for variable-frequency drive and harmonic suppression was proposed. This scheme is based on 12-pulse wave multiple rectification, ±15° phase-shifting transformers, and three-level H-bridge inverter, combined with integrated LC filtering and operation monitoring, to achieve source reduction of 5th and 7th harmonics and coordinated control of high-order harmonics. Field application shows that this scheme can effectively improve the waveform of the grid- side current, increase the power factor and the stability of equipment operation, providing an engineering reference for harmonic control of similar high-power variable-frequency loads.