The multicomponent analysis with Partial Least-Squares Method (PLS) using FTIR spectroscopy has been studied in this paper. In order to ensure the reliability of the prediction results, a criterionSOandSAis created in the PLS algorithm to conclude the similarity between the prediction samples and the calibration ones. An example for the simultaneous determination of Ethylbenzene, Styrene, o-Xylene, m-Xylene and p-Xylene is supplied. The experimental designs of the both the calibration and prediction samples are discussed as well as the significant factor number. With proper multivariate calibration conditions, the average mean relative error (MRE %) is 0.25 % and the average relative standard deviations (RSD%) for Ethylbenzene, Styrene, o-Xylene, m-Xylene and p-Xylene are 0.19, 0.15, 0.06, 0.44 and 0.13 %, respectively.