Abstract: A RFID composite events detection method based on rules engine was presented, which separated the expressions of composite events rules from corresponding code since present methods bind them together tightly and lead to bad scalability for application system. Since traditional rules engine method-Rete method always cache many partial matching results, while RFID data is usually constrained with time, an outdated data collection mechanism based on the life cycle of the partial matching was proposed to delete those expired partial matching segments in order to reduce the pressure of the Rete rule network. Simulation test result showed that the improved algorithm effectively relieved the pressure of the Rete rule network and was more appropriate for RFID composite events detection.