Comparison tests were carried out on extraction of Mg2+ in residual phosphoric acid by microemulsion to examine influence of the main experimental parameters such as oil/water,stirring speed,temperature and time of extraction on the extraction on Mg2+ in residual phosphoric acid.The experimental results show that the mass fraction of Mg2+ could be reduced from 2.3%~2.5% to less than 1%,when the extraction temperature is 35~40 ℃,extraction time is 4 h,stirring speed is 72 r/min and oil/water is 5.5∶1.