In the medium of 3 mol·L-1 hydrochloric acid, Cr(Ⅵ) oxidized As(Ⅲ) to be As(Ⅴ), the As(Ⅲ) content, which was left over, was determined by hydride generation-fluorescence spectrometry, giving that it was inversely proportional to Cr(Ⅵ) content. Based on the same principle and combined with potassium permanganate oxidation of Cr(Ⅲ) to be Cr(Ⅵ), the Cr(Ⅲ) was, therefore, determined. The sample digestion procedures and co-existing ions which might have interference were investigated. The instrumental operation parameters, reaction acidity and other influence factors were studied. Under optimum operation conditions, a good linear relationship was obtained in the range of 4.0～20 μg·L-1 Cr. The detection limit of the method was 2.5 μg·L-1. When the method was applied to milk analysis, a relative standard deviation(RSD, n=6) of 1.6%～2.7% was found. The recovery was 96.5%～104.2%.