Abstract: Experiments of extracting boric acid from high-Ca oilfield old brine in Qinghai were carried out.Influences of vari- ous factors，such as phase rate of extraction（volume ratio of organic phase to aqueous phase），volume fraction of extractant isooctanol，and phase rate of back extraction on the extracting and stripping were investigated.Results showed that when using sulfonated kerosene as the thinner，volume fraction of isooctanol was 50%，the phase rate of extraction was 1，the extraction time was 15 min，and extraction series were 3，the extraction rate of boron could reach 93.22%；when the back-extraction agent was  hydrochloric acid solution，its concentration was 0.1 mol/L，the phase rate of back extraction was 1，the stripping time was 15 min，and stripping series were 3，the stripping rate could reach 98.25%.Boric acid product was prepared by the processes，including extracting，stripping，evaporation in high temperature，and cooling in low temperature，dissolving again， cooling，filtering，washing，and drying，and its quality met the requirement of Industrial Boric Acid，GB/T 538—2006.

Key words: oilfield old brine, boric acid, extraction, stripping