Objective To identify the retention time of semen(stains)inside and outside the cadaver using Fourier Transform Infrared(FTIR)spectroscopy and chemometrics.Methods A simulated environment inside the porcine vagina was used to retain fresh semen for 0～168 hours inside and outside the body.Infrared spectroscopy data were collected,and chemometric methods including Principal Components Analysis(PCA)and Partial Least Squares(PLS)regression models were established.Results The infrared spectrum peak positions of semen(stains)inside and outside the body did not show significant changes over time.The PCA results showed good clustering relationships,and the predicted deviation value in the PLS regression model was 15.786 3 hours,with an R2 value of 0.922 4.The characteristic wavenumbers selected by the CARS algorithm were in the wavelength ranges of 1 000～1 180 cm-1,1 430～1 480 cm-1,and 1 700～1 760 cm-1.Conclusion Fourier Transform Infrared spectroscopy has the potential to identify the retention time of semen(stains)inside and outside the body,and there are differences in the degradation trends of semen(stains)inside and outside the body.