Abstract: An A. C. electrical desalter was used in the 50×104t/a atmospheric decompressor in Henan OilfieldRefinery which was put into production in 1992. Desaltertransformer tripping occurred frequently during operationas heavier crude oil were used and water content in crudeoil increased, resulting in unsmoothed operation and lowdesalting effect. Technical innovation of A. C. and D.C.electrical desalting were performed in 1996. Desalting anddewatering effects were significantly improved and met thestandards of salt content less than 3 mg/l, water contentless than 0.1% and oil content in oily water less than200mg/l. In addition, power consumption lowered about81%.