The bloodstain is the most common mark evidence in crime scene. The incident time can be inferred from bloodstain age; also it is closely related to postmortem interval. The estimation of postmortem interval has been the world's forensic problems. The bloodstain absorption in three different objects of glass, white paper and plastic film has been analyzed to explore the relationship between the postmortem interval and the bloodstain absorption by using the spectroscopy analysis technology in this paper. The study has found that the bloodstain absorption in the three objects presented a rising tendency as time goes on, there exists a positive correlation between bloodstain age and the postmortem interval.