AbstractIn order to improve the electric energy quality of switching power supply, through the theoretical analysis on the high frequency large-power rectification and the reverse switch supply theory, we conclude that the switch supply is the main polluting source of affecting the power energy quality. At the same time, we obtain that the contents of 3, 5, 7th-fold harmonic components in the switching supply is highest through the measurement of special harmonics test instrument. Other high-frequency harmonics also exist, but their proportions are rather low, as can be neglected. Therefore, the 3, 5, 7th-fold harmonic components of the switching supply are the major reasons leading to the system polluted. In order to eliminating the pollution of the harmonics produced by the switching supply to power grid and the side-effect to its own control system, this paper designs a general 3-phase passive filter instrument which can not only restrict harmonics, but also improve the power factor of the supply system. The test shows that the method can make the supply system to ideal effect, the contents of all kinds of harmonics become rather lower than the standard constituted by our country, and it also degrades the power harmonics and decreases the alternating current ripples greatly.