Adding hexodecyltrimethylammonium bromide(CTMAB) to improve solubility and delicacy, and using chromazurol S as a chromogenic reagent, and acetone as a stabilizing reagent, partial least-squares regression(PLS) was used to determine simultaneously trace amounts of Fe(III) and Al(III) in sythetic samples. Considering the stability of the rays, and the absorption properties of the two ingredients, seven wavelengths between 610 and 670 nm were selected for data collection. As a comparison, the methods of CPA and PLS were used respectively for analysing the data obtained from the experiment, and the results suggested that the latter was much better.