Abstract: There isn′t analysis method for free barium of barium sulphate in national standards.With the increasing use of barium sulfate，free barium content has become one of the important impurity indexes of barium sulphate product.Free barium was analyzed by flame atomic absorption spectrometry（AAS）.The influencing factors，such as the acidity when sample was dissolved，the gas flow，and selection of combustion-supporting gas，in experiment were discussed.The experiment was carried out under the conditions of the wavelength of 553.6 nm and with nitrous oxide as combustion-supporting gas.Through calculation relative standard deviation was at 1.6%~3.5%，standard sample recovery rates was at 99.13%~100.07%，sensitivity was 0.2，and barium detect limit was 0.2 mg/L.The deter-mination by AAS had the features of low interference and high accuracy.The experimental results were quite satisfactory and this method could meet the industrialized production requirements.

Key words: barium sulphate, free barium, AAS