Abstract: The magnesium hydroxide washing water which contains Ba↑2+ was used to react with sodium sulfate solution to prepare barium sulfate and the optimal conditions were determined：the mass fraction of superfluous sodium sulfate is 10%；reaction temperature is 50 ℃；reaction time is 30 min；thermal retardation and ageing time is 50 min；filter cake is washed by 5% sulfuric acid and then washed by electrodialytic water.This technology has been applied in industrial production and the quality of barium sulfate products met the first-grade standard in the standard of GB/T 2899—1996.With this technology the magnesium hydroxide′s washing water need not to be discharged，the problem of environmental pollution was solved and Ba↑2+ could be fully recovered.Therefore，the benefit of Mg(OH)↓2 production was greatly increased.