Abstract: Mathematical models for the n-hexane extracts and flow-rate of the molten fluid in Fourier tansform near-infrared diffuse-reflection spectrometric analysis of polypropyrene resin were constructed separately by using the partial least square (PLS) algorithm,and the optimum condition of the method of spectrum pretreatment,spectral range and main factor number were selected.The resolution coefficients (R2) for the mathematical models were found to be 98.03% and 96.65%.The mean square deviation of cross validation were 0.049 5 and 0.94 respectively.The results determined by the present method were in coincidence with those by standard methods.The method proposed in this paper showed its special features of high accuracy,rapidity and better repeatability.It is feasible especially for the quality analysis of samples in batches.