Abstract: The definition on the reliability of RFID (radio frequency identification) system which is based on the identification probability of tag and three kinds reliability index measures are given on the foundation of analysing RFID principle to evaluate reliability performance of RFID system comprehensively and objectively. In this paper, relations between three kinds reliability index measures are analyzed. Key factors including radio channel bit error rate and tags collision effects on identification probability affecting reliability of RFID system are analyzed, and the general models of calculating reliability of RFID system are presented. Simulation results show the models are suitable, feasible, and convenient to analyze, design, and evaluate reliability of RFID system.