Abstract: In an acetate buffer of pH 4.8,colored complexes were formed between DBPF and either of Cr(Ⅵ) or Cr(Ⅲ) in the presence of CTMAB and ethyl alcohol,with their absorption maxima at 580 nm and 576 nm respectively.The absorption spectra of Cr(Ⅵ) complex and Cr(Ⅲ) complex over-lapped seriously,making the individual determination impossible.Application of the three layer ANN to the photometric speciation analysis of Cr(Ⅵ) and Cr(Ⅲ) by the color reaction mentioned above,the problem of spectra overlapping was solved,and the determination of Cr(Ⅵ) and Cr(Ⅲ) was carried out simultaneously.The apparent molar absorptivities for Cr(Ⅵ) and Cr(Ⅲ) were found to be (ε580) 1.13×105L·mol-1·cm-1 and (ε576) 8.96×104L·mol-1·cm-1,with their linearity ranges of 0-0.287 mg·L-1 and 0-0.131 mg·L-1 respectively.By using the improved back propagation algorithm,not only falling into part minimum in the training procedure was avoided,but also its convergence speed and spreading ability were raised.Recovery and precision of the method was tested by analyzing several simulated water samples and substantial water samples of tap water and water from East Lake.