Estimation of the postmortem interval (PMI) is a practical task in daily forensic casework. Researches on PMI is an important practical project in forensic field. Estimation of the time since death is influenced by internal and external, antemortem and postmortem factors, thus the old methods have limitations. Fourier transform infrared (FTIR) spectroscopy has been applied to study the pure protein, nucleic acid and carbohydrate and to detect the changes in complex cells and tissues. At present because the powerful software has could be used to achieve the spectrum transformation, smoothing, baseline correction and normalization, it is possible to analyze the samples quantitatively with the FTIR which has been applied in the biology and clinical medicine. This paper has reviewed the mechanism of FTIR and its application in biomedicine. The postmortem FTIR spectral changes were also discussed, which showed its potential for estimating PMI.