Abstract: According to the characteristics of infrared absorption of the copolymer of propylene-ethylene,proper wavelengths of infrared absorption band of propylene and ethylene were chosen and propylene monomer was determined by Fourier transform infrared spectrometry (FTIR).Samples of same and homogenuous thickness were propared by an universal press.Standard curve was prepared by taking the mass percentage of propylene monomer as the ordinate and the peak area ratio of A1 165/A720+730 as the abscissa.Values of absorbance were measured with FTIR spectrograph.The results obtained were checked with the results found by 13CNMR,giving values of relative errors less than 2%.In analyzing 5 samples by the proposed method.RSD′s (n=6) calculated were in the range of 0.47%-1.1%.