A new method，based on the composite application of the iterative algorithm，the partial least squares（PLS） and the ultraviolet spectrophotometry，was presented for the simultaneous determination of three tolualdehyde isomers among the six components prepared by indirect electrosynthesis with the xylene.The PLS was enchased to the iterative algorithm to obtain the approximation through the interactive calculations，which could improve the spectral identification ability of the products.The proposed method was applied in the simultaneous determination of three tolualdehyde isomers in four simulating samples with satisfactory results.The mean recoveries of o-tolualdehyde，m-tolualdehyde and p-tolualdehyde were 101%，100% and 101%，respectively，and root mean square errors of prediction（RMSEP） were 0.214，0.148 and 0.057，respectively.The practical application to five group electrosynthesis tolualdehyde products showed that the average recoveries were 106%，92% and 100% for o-tolualdehyde，m-tolualdehyde and p-tolualdehyde，respectively，and the relative error was less than 19.7%.The results were compared with those obtained from the HPLC method with no significant difference.