This paper presented an application of mid-infrared (MIR),near-infrared (NIR) and Raman spectroscopies for collecting the spectra of 31 kinds of low density polyethylene/polyprolene (LDPE/PP) samples with different proportions.The different pre-processing methods (multiplicative scatter correction,mean centering and Savitzky-Golay first derivative) and spectral region were explored to develop partial least-squares (PLS) model for LDPE,their influence on the accuracy of PLS model also being discussed.Three spectroscopies were compared about the accuracy of quantitative measurement.Consequently,the pre-processing methods and spectral region have a great impact on the accuracy of PLS model,especially the spectra with subtle difference,random noise and baseline variation.After being pre-processed and spectral region selected,the calibration model of MIR,NIR and Raman exhibited R2/RMSEC values of 0.990 6/2.941,0.997 3/1.561 and 0.997 2/1.598 respectively,which corrsponding to 0.887 6/10.15,0.849 3/11.75 and 0.875 7/10.67 before any treatment.The results also suggested MIR,NIR and Raman are three strong tools to predict the content of LDPE in LDPE/PP blend.However,NIR and Raman showed higher accuracy after being pre-processed and more suitability to fast quantitative characterization due to their high measuring speed.