Accurate estimation of postmortem interval (PMI) is one of the most important and difficult issues in forensic medicine. After death, the tissues autolyze and biomacromolecules degrade. DNA concentration decreases gradually with linear relationship with PMI. The housekeeping gene mRNA, for example beta-actin, GAPDH, has certain stability and can be used to PMI estimation as internal standard. This paper reviews the research progress and problems about DNA, RNA and proteins in the estimation of PMI in order to provide guidance for forensic pathology.