To retrospectively analyze homicide cases of death after injection and provide reference for forensic identification. Six homicide cases of death after injection which were investigated by the Criminal Investigation Team of Shanghai Public Security Bureau were collected and analyzed, including case situation, scene investigation, autopsy and other materials. The 6 cases were premeditated crimes, 5 cases took place in private spaces, and 5 cases involved the victims approached by suspects' decoy. There were no obvious abnormalities at the scene of the 6 cases. In 6 cases, the victim's body surface injury was mild or no, lividity color was abnormal, and the needlestick injury showed different manifestations from conventional medical measures. Death after injection is a highly concealed crime and easy to be ignored. For the suspected injection injury found in autopsy, it is necessary to carefully examine, identify and analyze, be alert to the situation of injecting poison (drug) and do a good job in evidence fixation and material extraction.