Abstract: A rapid and sensitive method for using a microcolumn of activated alumina in FIA manifold to separate and preconcntration Cr(Ⅵ) from Cr(Ⅲ) in the sample of industrial waste water and to determine with sepctrophotometric detection has been developed. The total Cr was determinated under same conditions after the sample was treated with basic KMnO₄, and the concentration of Cr(Ⅲ) was finally obtained by taking a difference. The sampling rate was 36 samples/h, the range of the recoveries was 100%~200% and the relative standard deviation at 2 and 0.1mg/L were 0.8 and 5.3%, respectively.