Abstract: The characteristic of volatility and easy-to-lose deficiency increases the difficulty of boron analysis work.The fast accurate determination of the micro-boron (B<SUP>3+</SUP>) in brine,has become a reseach topic of analysts.B<SUP>3+ </SUP>in brine can be extracted by the mixture of 2-ethyl-1,3-hexanediol and methyl isobutyl ketone (MIBK).And B<SUP>3+&nbsp;</SUP> in organic phase can be directly determined by atomic absorption&nbsp; spectrometry (AAS).The influencing factors,such as wave length,combustion-supporting gas,vessel,and coexistent ions were discussed.The determination by AAS had the features of low interference and high accurancy,and the experimental data were quite satisfactory.The experiment was carried out under the conditions of wave lengths of 249.7 nm and with nitrous oxide as combustion-supporting gas.Relative standard deviation of 2.8%-5.6%,standard sample recovery rate of 98.2%-103.3%,sensitivity of 0.2 and boron detection limit of 5 mg/L have been obtained through calculation.